Andy Murray has pulled out of his Washington Open quarter-final on Friday after only finishing his last-16 win at 03:02 local time earlier the same day.
The 31-year-old Briton, playing in his third tournament after hip surgery, was due to play Australian Alex de Minaur.
The former world number one broke down in tears after beating Romanian Marius Copil in the early hours of Friday.
Murray has also withdrawn from next week’s Rogers Cup in Toronto to continue his recovery.
The Scot says he will now focus on preparing for the Cincinnati Masters, which starts on 13 August.
“I’m exhausted after playing so much over the past four days, having not competed on the hard courts for 18 months,” Murray said.
“I also need to be careful and to listen to my body as I come back from a long-term injury.”
Murray won three matches in four days at the Citi Open in Washington, sobbing on court after completing his last-16 victory over Copil at 03:02 local time on Friday.
He made his comeback after an 11-month absence at Queen’s in June and also played at Eastbourne before deciding he was not fit enough to compete at Wimbledon last month.
Speaking after beating Copil, Murray said: “My body doesn’t feel great right now. Finishing matches at three in the morning isn’t good for anyone involved in the event – players, TV, fans, anyone.
“When you’re expected to come back and perform the next day, I think that’s unreasonable.”
Before his withdrawal, tournament director Keely O’Brien responded to Murray’s comments by claiming the Briton pulling out of the quarter-final would send out a negative message.
“I hope that Andy really takes into consideration this role in his sport and as a global role model to guys and girls on the tour and kids around the world that when things are difficult and tough and the conditions aren’t great that it’s not OK to just give up,” O’Brien told the Washington Post.
“I hope we see him on court tonight fighting like he did last night, because that, I believe, is the right message for anyone in this sport.
“Certainly if he can’t play because of his injury that’s one thing. But he’s a fighter, and he doesn’t give up, and he needs to have everyone see that.”
After Murray announced his withdrawal, O’Brien said: “I sincerely respect his decision and know that his health and recovery process is his top priority, as it should be.”
‘I need to be smart with my rest and recovery’
After pulling out of Wimbledon on the eve of the tournament, Murray turned his attention to building his fitness for the American hard-court season.
The three-time Grand Slam champion was given wildcards at Washington, Toronto and Cincinnati, all important tournaments leading up to the US Open.
The fourth and final Grand Slam of the year starts at Flushing Meadows in New York on 27 August.
Following wins in Washington over Mackenzie McDonald, Kyle Edmund and Copil, all three-set matches, Murray decided it would be better to miss the Rogers Cup – which he won in 2009, 2010 and 2015 – and go straight to Cincinnati.
“I need to be smart with my rest and recovery,” Murray said.
“My plan is to head to Cincinnati early next week. Appreciate all the support this week in Washington, it’s amazing to be back playing.”