Murray underwent hip re-surfacing surgery at the start of 2019 and resumed playing doubles in June before returning to singles action in August.
He did not compete at the US Open in September but won the title in Antwerp in October -- his first on the ATP Tour for two years.
Murray, 32, has not played a competitive match this year because of bone bruising near the site of his surgery.
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With tennis unlikely to return until at least late July because of the coronavirus pandemic, the Scot has plenty of time to get himself 100 percent fit for when play resumes.
Yet Rusedski says it will be tough for two-time Wimbledon champion Murray to regain his former place in the top echelons of men's tennis alongside Roger Federer, Rafa Nadal and Novak Djokovic.
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What did Rusedski say?
"The good news for him is that he's had more of a rest at this point," Rusedski told Sky Sports on Sunday. "Hopefully his body comes back, but to challenge week in week out with Nadal, Federer, Djokovic, (Stefanos) Tsitsipas is going to be hard.
"Can he win matches? Can he possibly win a Tour event? Yes, he can do so. But to win Slams, that's three out of five sets, seven matches, that's a little bit difficult. It's possible he can get to a quarter-final, fourth round, but to go all the way with the surgeries he's had, that's a big ask.
"But I hope he proves me wrong, like he's done on several occasions."
Where is Murray now?
Former world number one Murray is now ranked at 129. Next week he will swap his racket for a controller as he plays in the 'virtual' Madrid Open, featuring 32 of the world's best players including Nadal and Dominic Thiem.
Our view - can he come back?
Rusedski is probably right, but the Big Three he is chasing have all got remarkable comeback or survival stories of their own.
Roger Federer continues to play at the highest level, winning Grand Slams of his own, at 38 years old and does not yet appear ready to retire, despite taking a couple of years in semi-retirement to extend his career.
Novak Djokovic had to make a huge change to his diet, giving up gluten, to achieve his legendary stamina and finally emerge as tennis' current undisputed number one competitor.
Rafael Nadal has occasionally looked like he is on his way out, too. His repeated injury problems with his knees and shoulder might have sunk less determined competitors.
While things look bleak for Murray, the pause in the season gives him the chance to recover unfettered at his own pace, and while other people struggle to walk following a hip resurfacing, it may not be out of the question that he could make a comeback of his own, however unlikely.
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