Andy Murray will prioritise rest before beginning his preparations for his next tournament in Cincinnati in just over a week.
The three-time grand slam champion pulled out of the Citi Open ahead of his scheduled quarter-final clash with Australian Alex de Minaur in Washington on Friday night.
The former world number one cited exhaustion for his decision following a gruelling week that had seen him taken to three sets in all three of his matches and spend more than eight hours on court.
The 31-year-old, who only finished his third-round win against Marius Copil at 3am on Friday morning, said in a statement on the ATP website: "I won't be able to play my match tonight. I'm exhausted after playing so much over the past four days, having not competed on the hard courts for 18 months.
"I also need to be careful and to listen to my body as I come back from a long-term injury. I'm gutted not to be playing and I'd like to thank the tournament and all the fans."
Tournament director Keely O'Brien had earlier caused controversy with comments to the Washington Post encouraging Murray to play.
O'Brien said: "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, it's not OK to just give up.
"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."
With Murray regarded as one of the great fighters in tennis, and given the delicate nature of his recovery from hip surgery, the comments seemed particularly ill-judged.
Neither Murray nor his team have responded publicly but it is understood they were distinctly unimpressed and have made their feelings known.
O'Brien struck a different note in an official statement following Murray's withdrawal, saying: "I am so grateful that Andy, an incredible champion, came back to D.C. to begin what we all know will be a great comeback.
"I sincerely respect his decision and know that his health and recovery process is his top priority, as it should be. We all wish him great success for the rest of the summer and look forward to him coming back to Washington next year."
It was Murray's first hard court tournament since March 2017, and he added in his statement: "There are lots of positives to take from this week, so I'll take some time to rest and recover - I won't play in Toronto next week - and then head to Cincinnati early to prepare and get ready."
Murray had earlier announced he would not be playing in next week's Rogers Cup, which would have been his first Masters tournament since last spring.
He will instead play next at the Masters event in Cincinnati, which begins a week on Monday, as he continues his build up to what is expected to be his first grand slam tournament since last year's Wimbledon at the US Open later this month.