Andy Murray says he 'can't say with any certainty' he will ever be able to play a sustained spell of tennis again.
Murray is attempting to return from a hip injury that decimated his career while he was world number one in 2017.
He has attempted multiple comebacks, and although hip resurfacing surgery appears to have removed the pain whilst playing, it has seemed to make him more susceptible to other injuries.
Murray was forced to withdraw from the Olympics singles in Tokyo last month, although he did return at the Cincinnati Masters with a first-round win over Richard Gasquet.
The three-time Grand Slam winner revealed it was a tear in his quad behind his latest setback, and that kind of injury is something very new to him.
"I have never had any muscle injuries in my career, so I didn't really know what they felt like," Andy Murray told Sky Sports. "It was a difficult one.
"It was hard and frustrating again to have to miss another big event.
"Granted, I got the opportunity in doubles and we were close to getting into the medal rounds.
"We were potentially going to go to Canada, but just felt like maybe needed to have a few more days of rehab to make sure the quad was really fine and recovered before starting to play again.
"Here, I feel good again, but as I said earlier in the year, I can't say with any great certainty that I'm going to be feeling good for three, four months in a row."
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