Andy Murray was forced to withdraw from his Queen's Club Championship match against Jordan Thompson on Wednesday with a back injury.
Murray, 37, looked uncomfortable walking to the court before the match started. He then required treatment on his lower back from his trainer just a few minutes into the round-of-16 match.
Despite attempting to play on, Murray was forced to retire with Thompson leading 4-1.
"I didn't get the right side of my back treated after the French Open. All tennis players have degenerative joints in the back but it's all predominantly been left-sided for me, for pretty much my whole career," Murray told reporters.
The 37-year-old Murray, who considered retiring in 2019 due to a hip injury, hopes to play at Wimbledon with rest and treatment and has been named to represent Great Britain at the Olympics in Paris this summer.
He has won Wimbledon twice but has not got past the third round at the grasscourt tournament in the last three years.
"Maybe there's something which can be done between now and then with my right side, will have a scan tomorrow and re-check and see what can be done," he said.
The former world number one, a three-times Grand Slam champion, had celebrated his 1,000th tour-level singles match by beating Alexei Popyrin of Australia 6-3, 3-6, 6-3 in the first round.
But Murray said he felt discomfort in Tuesday's match.
"It didn't feel too dissimilar to yesterday, slightly worse," he added.
"If it felt like that before the match, I wouldn't have played but from my pre-match warm-up to the match court, I wish I hadn't gone on court to be honest."
Earlier in men's doubles, British duo Jack Draper and Cameron Norrie were knocked out in the round of 16 in two sets.
The pair went down 6-4, 6-4 to Edouard Roger-Vasselin and Santiago Gonzalez.
At the Birmingham Classic, Heather Watson and teammate Greet Minnen advanced to the quarterfinals of the women's doubles competition with a 6-3, 6-2 win over Erin Routliffe and Gabriela Dabrowski.
Watson and Minnen will face Miyu Kato and Zhang Shuai in the quarterfinal on Thursday.
Information from Reuters contributed to this report