Brad Gilbert says it will be a "big challenge" for Andy Murray to get back to his best after undergoing surgery to resolve a "very concerning" hip injury.
The three-time grand slam champion went under the knife in Melbourne, where he had hoped to play in the Australian Open but withdrew from the first major of the year.
Murray has not played competitively since Wimbledon, but is targeting a comeback in the grass-court season following an operation which he hopes will rid a long-standing problem.
Gilbert, the Brit's former coach, believes the 30-year-old will find it very difficult to return to the peak of his powers.
The American told Omnisport: "He has not played a match since Wimbledon and it must have been a quandary as to whether to get surgery done straight away or play on.
"It is not going to be easy at all for him to get back to the top and especially tough to come back after a year out, it seems a short time to recover from hip surgery. Murray and [Novak] Djokovic have clearly seen Roger Federer and Rafael Nadal come back from time out and go 'boom' and felt that is the way to go.
"He came back in 2013 after I think four or five months out with a back injury. Obviously he was younger then, but he is six years younger than Federer and younger than Nadal and we know what they did last year.
"It is very concerning for Murray and will be a big challenge for him, but he would not have had the surgery if it was not totally necessary and he can take great inspiration and heart from what Federer and Nadal have done. I certainly hope he can get right back to the top."
- Gilbert will be working in his role as an ESPN analyst at the Australian Open.