With the transfer window back and in full swing, we take a look at a selection of incredible deals that could have been.
Giuseppe Meazza (youth to AC Milan, 1923-24)
Perhaps the finest player Italy has ever produced, Meazza was the inspiration behind Italy's World Cup successes of 1934 and 1938. He spent the first 13 years of his career with Inter Milan, scoring 31 goals in his debut season and helping the club, then known as Ambrosiana, to three league titles and one Coppa Italia.
However, Meazza had been an AC Milan fan as a youth, and at 13 years old they rejected the chance to sign him due to a concern that he appeared too frail. An Inter scout later chanced upon him while playing in the street, and he would go on to become the club's finest player.
He did finally make his way to Milan in 1940 but by that stage was suffering with blood clots and was all but finished as a player; he looked, in the words of the legendary journalist Gianni Brera, "as if he was on the verge of dropping dead any minute".
Despite that underwhelming stint, the clubs were united in their admiration for the forward and, following his death in 1979, they reached a rare accord: the San Siro was renamed the Stadio Giuseppe Meazza in his honour.
Alfredo Di Stefano (Millonarios to Barcelona, 1953)
One of the finest players ever to have lived, Di Stefano was the leading star as Real Madrid dominated the early years of the European Cup and became established as the world's finest club. However, Barcelona had also been in negotiations to sign the player and indeed there had been an agreement at one stage that would see Di Stefano spend alternate years between the two Spanish clubs.
Ultimately, Barca withdrew from the deal in circumstances that remain the subject of debate to this day. To read the full story of his transfer, click here.
Garrincha (Botafogo to Inter Milan, 1963)
For many, he was the leading star at the World Cups of 1958 and 1962 but, like Brazil team-mate Pele, his club career was spent entirely in the Americas.
It might have all been different: in June 1963, Inter Milan agreed to pay Botafogo £400,000 - which would have smashed the world transfer record at the time - and successfully negotiated terms with the player. However, the 28-year-old, having suffered a knee injury earlier in the year, was unable to pass a medical.
He was still having trouble with his knees in August and, by November, with the player's disciplinary problems proving a major problem, Botafogo dropped their asking price to around £115,000. It was not until 1966 that he was finally offloaded to Corinthians.
Diego Maradona (Argentinos Juniors to Sheffield United, 1978)
Sheffield United manager Harry Haslam spotted the 17-year-old Maradona on a scouting trip to Argentina in 1978 and immediately set about negotiating a deal. He managed to agree a fee, with contemporary reports suggesting he negotiated Argentinos Juniors down from £1 million to £600,000. Nonetheless, the Blades were then a lowly Second Division club, and they were unable to pay it; they instead turned to River Plate midfielder Alex Sabella for a club-record £160,000. The Blades were relegated to the third tier that season, despite Sabella's efforts.
In 1980, Juventus were also thwarted in an attempt to sign Maradona, who signed for Boca Juniors in 1981. In March 1982, Arsenal were reported to be lining up a £4 million bid, which prompted one Labour MP to lodge a question to the sports minister in the House of Commons over the "scandalous" fee. Maradona, who had expressed a willingness to move to Highbury, ended up going to Barcelona shortly afterwards for £5 million.
Johan Cruyff (free agent to Leicester City, 1981)
Having enjoyed success with Ajax and Barcelona, Cruyff had expressed an interest in playing in England. Arsenal were interested in 1976 and two years later Chelsea, though some £2 million in debt, felt compelled to offer the Dutchman a game-by-game deal. "That would be no good at all," Cruyff, at that stage in retirement, said.
He did come out of retirement to play in the US, and in February 1981 Leicester City believed they had signed the 33-year-old. "All that remains to be settled is the formality of sorting out the player's business affairs," manager Jock Wallace said. "I am absolutely delighted. He will be the biggest draw in the First Division."
The following day, Wallace announced that Cruyff had instead agreed to join Levante, in the Spanish second tier, after they offered him 50% of their gate receipts.
Paul Gascoigne (Newcastle United to Manchester United, 1988)
In 2008, Sir Alex Ferguson told interviewer Sir David Frost that the failure to sign Gascoigne was the biggest disappointment he had endured in the transfer market, describing the midfielder as "the best player of his era in English football".
Tottenham Hotspur had actually moved first for the player in July 1988 but Ferguson, having seen Gascoigne make a mockery of his midfield in March 1987, was determined to take him to Old Trafford. The 21-year-old visited the United academy and resolved to make the move, but Spurs chairman Irving Scholar refused to accept defeat.
"I was thinking Man U is a massive club, so I thought I'll go to Man U - they offered us big wages," he told Life Stories in 2011. "Alex Ferguson says, 'I'm going on holiday. I'll see you when I get back'. 'Okay, enjoy your holiday. I'll sign.'
"And so as I was driving to Manchester I get a phone call from Irving Scholar: 'Paul, we'll give you £2,500 a week. Not only that, we'll buy your dad a house', so I said, 'Ma and dad, Spurs are gonna buy us a house. What do you think?' 'Sounds good, son.' So I said, 'All right then - yes'."
Gascoigne revealed last year that Ferguson, never one to take such matters lightly, subsequently wrote to the midfielder to express his view that he was a "fat bastard".
Eric Cantona (Nimes to Sheffield Wednesday, 1992)
Already well known as France's enfant terrible, Cantona had announced his retirement in December 1991 after he was banned for a month for throwing the ball at a referee. His club, Nimes, had acceded on condition that Cantona pay £700,000 to annul his contract, but he needed to play to raise the funds and so - on the advice of his psychoanalyst, among others - he decided to join a club in England.
Sheffield Wednesday manager Trevor Francis, having taken a recommendation from France boss Michel Platini, agreed to take Cantona on trial, with a view to a £100,000 loan deal with the option to buy for £800,000.
Cantona arrived late for his trial and, after six days with the club, Francis asked him to stay another week as he had yet to see the player perform on grass due to weather conditions. Cantona, 25, walked out. "His lawyer told me he is a big star in France and would lose face if he stayed for another week on trial," Francis explained. "If he wants to come back, he is very welcome."
Cantona announced he was heading back to France, but Howard Wilkinson, manager of Yorkshire rivals Leeds United, decided to step in and tied up a deal almost immediately. "I've never signed a player without seeing him in the flesh, but I've seen enough of him on video," Wilkinson explained. The forward added: "My behaviour has been irreproachable and highly honourable."
Zinedine Zidane (Bordeaux to Blackburn Rovers, 1996)
In the spring of 1996, the Lancashire Telegraph broke the news that Blackburn manager Ray Harford had been on a scouting trip to see both Zidane and Christophe Dugarry. He had been impressed, but Rovers' munificent owner, Jack Walker, is reported to have asked: "Why do you want to sign Zidane when we have Tim Sherwood?"
Sherwood himself explained in 2009: "I remember Dugarry and Zidane talking to Ray Harford and that was the time when we should have kept building and kept looking to improve. Instead we brought in fringe players. I think Jack Walker thought: 'We won it with the players we have already got, so we do not need to speculate'. He made very few mistakes but that was one."
Blackburn, it seems, were not alone in making a mistake on Zidane: agent Barry Silkman claims Newcastle missed out on the Frenchman that same year. "I offered him to Newcastle at the beginning of the 1996 season for £1.2 million, and they watched him and said that he wasn't good enough to play in the First Division, which is the Championship now," Silkman later told Sport.co.uk.
Zidane finally agreed a move to Juventus that summer.
Xavi Hernandez (Barcelona to AC Milan, 1999)
He has been the foundation of Barcelona's passing game, but AC Milan vice-president Adriano Galliani said the Rossoneri were "really an inch from taking Xavi" in 1999.
Certainly he was close to making the move, with Xavi having felt his opportunities at the Camp Nou may be restricted by the presence of Pep Guardiola in the midfield. Xavi himself has said that it was "actually Barca which decided that I had to stay", but it appears his mother, Maria, also played a part.
"We were offered a villa and more than €1 million for five seasons," she told La Vangardia. "Trips would be paid for, a job for my husband. We analysed it as family - Xavi is the third of four children, and they were all against me. Everyone wanted him to take this opportunity and also complicating things was the fact that he seeing Pep Guardiola playing in his position. I said: 'If he leaves, I will divorce.' The final decision was still taken by him, however."
Xavi also revealed in 2011 that he had rejected a move to Manchester United early in his career, saying: "I have always felt a real attachment to English football and Manchester United would be my club in England. I thought about going to United but I dug my heels in. I was obstinate and I said to myself, 'I need to prove myself here'."
Ronaldinho (Gremio to St Mirren, 2001)
In March 2001, St Mirren - then at the foot of the Scottish Premier League - faced the prospect of signing Brazilian legends past and present.
Bebeto, the 1994 World Cup-winning striker, was available on a free transfer and the 37-year-old expressed an interest in moving to Paisley, but as Saints boss Tom Hendrie explained at the time: "The agent said that his reputation should be enough for us to sign him without seeing him and we simply couldn't get ourselves into that position."
St Mirren were, though, highly keen to bring in Ronaldinho. The forward had already agreed a summer switch to Paris Saint-Germain and his club, Gremio, had frozen him out as a result. As a solution, a loan switch to Scotland was proposed, with PSG keen to allow him to acclimatise to European football.
Hendrie said at the time that Ronaldinho was "willing to come and play for us before going on to PSG", but a fake passport scandal put paid to the deal. The manager added: "There was a legal problem at the club he was at. Because of the problem, the Brazilian FA would not release the player's international clearance in time for us to register him ahead of the deadline."
St Mirren were unable to lift themselves from the foot of the table and were relegated with -40 goal difference.
Cristiano Ronaldo (Sporting to Arsenal, 2003)
Famed for his ability to spot potential, Arsene Wenger recognised the quality of the 18-year-old Ronaldo when he appeared for Portugal as they won the 2003 Toulon Tournament. Ronaldo was sufficiently interested in the switch to pay a visit to North London, but Arsenal ultimately decided that he was worth little more than £4 million and decided not to take the risk.
In August, he signed for Manchester United for £12.25 million.
"I had Ronaldo at the training ground," Wenger revealed in 2008. "I showed him around and I gave him a shirt - it had got his name on the back - but in the end it was a question of the amount of transfer fee between the two clubs. Of course, he has proved to be a bargain, but the price that we discussed was in fact much lower - it was divided by three."
Wenger was philosophical over the matter. "I saw that he was an exceptional talent but we could not predict that he would become the player that he is," he said. "At the end of the day, I wanted him to be here, but the most important thing is he made a career. He went to Man United and did that."
Ronaldo has also confirmed that a deal was close, saying: "I met Arsene on three occasions and one of those times was with my mum, who wanted to hear what he was proposing.
"The contact we had with him and Arsenal meant it was very close to being a done deal. Really, we were within touching distance. Wenger remains someone that I still have immense esteem for and it's clear that he's a really intelligent football guy."