It can happen to any team, at any time, but right now it is Premier League champions Liverpool who are battling their way through a bona fide injury crisis.
With a crucial game against Leicester City coming up on Sunday, a game in which the Reds could set a new club record by going 64 home league games unbeaten, it's likely that manager Jurgen Klopp will be without at least five and possibly as many as eight of his first-team players.
It's in defence where the crunch is most acute, with Klopp having just one senior centre-back to pick from at the moment, but there are issues all over the pitch.
Here is the full extent of the selection woes at Anfield as things stand, assuming nothing else goes wrong on Merseyside between now and 7:15 p.m. on Sunday.
Jump to: Centre-backs | Full-backs | Midfielders | Forwards
CENTRE-BACKS
Virgil van Dijk
What's the injury?
Van Dijk recently underwent surgery to repair the anterior cruciate ligament damage that forced him to limp out of the Merseyside derby at Everton on Oct. 17.
How long will they be out?
Liverpool confirmed last week that the Dutchman's procedure was a success but he's still expected to miss much of the remainder of the season.
Who can replace him?
As the only fit senior centre-back at the club, Joel Matip will stand in for Van Dijk -- though it's a tall order replacing an ever-present pillar who played all 3,420 minutes of last season's title win.
Joe Gomez
What's the injury?
Gomez sustained a serious knee injury while training with England ahead of their recent friendly against the Republic of Ireland.
How long will they be out?
While Liverpool have since confirmed that Gomez underwent a successful surgery to repair his ruptured patella tendon, the club refused to put a timescale on his return. Instead, the Reds simply stated that while the versatile defender will make a full recovery, the issue is "likely to rule him out for a significant part of the remainder of 2020-21."
Who can replace him?
Dejan Lovren would perhaps be the ideal candidate, but unfortunately he was sold to Zenit St Petersburg back in July. Instead, it looks like 23-year-old Nat Phillips will continue to deputise at centre-half after impressing on his debut against West Ham, despite originally being told he would be leaving Liverpool in the last transfer window.
Fabinho
What's the injury?
Of course, defensive midfielder Fabinho had been covering at centre-half due to the Reds' mounting injury woes. However, he lasted for just 30 minutes of Liverpool's home Champions League outing against FC Midtjylland on Oct. 27 before having to come off with a hamstring problem. The Brazilian underwent a series of scans which subsequently saw him ruled out until after the international break.
How long will they be out?
Klopp has since confirmed that Fabinho's muscle injury is only a "minor" issue and that he should be in line to return at some point soon.
Who can replace him?
Teenager Rhys Williams was initially brought in as a replacement for Fabinho, but it looks like he too is now facing a fitness battle after taking a knock on England under-21 duty.
Rhys Williams
What's the injury?
Williams replaced Fabinho against Midtjylland and then started at centre-back against Atalanta but was kept out of the fray for England U21s after manager Aidy Boothroyd confirmed the 19-year-old was struggling with a "stiff hip."
How long will they be out?
It was felt to be in Williams' best interests to release him from international duty and return back to Liverpool to convalesce, though there have been no further updates on his condition since.
Who can replace them?
Signed from PEC Zwolle for £4 million last summer, Sepp van den Berg is an 18-year-old centre-half who has been playing with the Liverpool U23s. Van den Berg could potentially be used to plug the gap, though it would appear the young Dutchman isn't really on Klopp's first-team radar despite the spiralling injury crisis he faces.
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FULL-BACKS
Trent Alexander-Arnold
What's the injury?
Alexander-Arnold was initially taken off during the 1-1 draw against Manchester City with a hamstring injury but has since succumbed to a further calf tweak that ruled him out of taking part in all three of England's fixtures during the international break.
How long will they be out?
The right-back has stepped up his rehab schedule at Liverpool's new state-of-the-art training facility, but is still unlikely to be ready to face Leicester City this weekend. In fact, there are fears that he may actually miss the Reds' next three Premier League fixtures as well as the remainder of their Champions League group-stage campaign, which ends with a trip to Danish side FC Midtjylland on Dec. 9.
Who can replace him?
Thankfully, in James Milner, Liverpool can call on a trusty stalwart to fill in almost anywhere on the pitch -- with the veteran utility man coming off the bench to replace the injured Alexander-Arnold at the Etihad. There's also Neco Williams, though the 19-year-old right-back has injury concerns of his own after sitting out of Wales' game against Republic of Ireland on Sunday with a sore foot.
Andy Robertson
What's the injury?
Robertson played all 120 minutes for Scotland as they qualified for Euro 2020 with a hard-fought playoff against Serbia, then sat out against Slovakia three days later with a tight hamstring -- causing Liverpool fans to collectively hold their breath.
How long will they be out?
The left-back then returned to play 90 minutes for the Scots against Israel in the third of their international fixtures, so it's looking likely that he'll be in fine fettle for Sunday's game against Leicester.
Who can replace him?
While it looks like Robertson will be fine to face the Foxes, reserve left-back Kostas Tsimikas -- signed in the summer from Olympiakos -- is ready to serve as back-up if called upon.
MIDFIELDERS
Jordan Henderson
What's the injury?
Club captain Henderson pulled out of the latest England squad after being withdrawn at half-time during the Nations League game against Belgium on Sunday after feeling "a bit of tightness" in his leg.
How long will they be out?
Henderson is now a considerable doubt for Liverpool's game against Leicester, though the club will be assessing him all week in the run-up.
Who can replace him?
Georginio Wijnaldum will likely run the Reds' central midfield against the Foxes with Naby Keita alongside him and perhaps the chance for 19-year-old youngster Curtis Jones to graduate from the bench.
Thiago Alcantara
What's the injury?
Midfield maestro Thiago has also been ruled out since the derby against Everton last month after suffering a knee injury from a lunging challenge by Richarlison that earned the Brazilian a red card.
How long will they be out?
The Spanish string-puller has been seen back in training in recent weeks with Liverpool optimistic he will be back in action sooner rather than later. Klopp has confirmed that Thiago is "getting closer" to a return, but it remains to be seen whether the 29-year-old is fit enough to take part against Leicester.
Who can replace him?
While there is nobody quite of Thiago's ilk in the Reds' squad, it will fall to Wijnaldum and Keita to pair up in midfield together. Who knows, maybe Xherdan Shaqiri might even get a look-in?
Alex Oxlade-Chamberlain
What's the injury?
Oxlade-Chamberlain has suffered terribly with injuries during his career and the 27-year-old is in the midst of another extended layoff after suffering another knee problem during preseason training.
How long will they be out?
Thankfully, it looks like The Ox is on the mend with a recent Instagram update boosting hopes that he is getting close to fitness after three months on the sidelines.
FORWARDS
Mohamed Salah
What's the injury?
Not an injury, as such, but Salah is quarantined at his hotel in Egypt after testing positive for coronavirus last Friday ahead of his county's Africa Cup of Nations fixture against Togo, a week after attending his brother's wedding in Cairo.
How long will they be out?
Salah's symptoms were said to be "mild" and it was reported that if he could return a negative test on Wednesday of this week, he'd be allowed to return to Liverpool -- though he would then have to begin a 10-day period of self-isolation. Unfortunately, the forward tested positive once again and therefore he must remain in El-Gouna, definitely ruling him out of the Reds' upcoming fixtures.
Who can replace him?
It seems likely that Klopp will opt for a front three of Sadio Mane, Roberto Firmino and Diogo Jota for the visit of Leicester to Anfield. After all, he fielded all four of them fromt he start against Manchester City in Liverpool's last game before the international break.