Roger Federer admitted on Sunday he was shocked that tennis was to lose "legend" Andy Murray this year while long-time friend Novak Djokovic said the bombshell news had "hurt" him.

Both paid tribute to the former world number one on the eve of the year's first Grand Slam with Federer adding that the Scot should be "incredibly proud" of what he had achieved.

Murray on Friday admitted that his chronic hip injury had not been eased by surgery a year ago.

He then choked back tears and broke down as he revealed that he hoped to end his storied career at Wimbledon, but the Australian Open beginning on Monday could be his last event because the constant pain was so bad.

"I was disappointed and sad, a little bit shocked, to know now that we're going to lose him at some point," Federer told reporters.

"But we're going to lose everybody at some point. It's just now that it's definite," he added, acknowledging that the era of the "Big Four" — himself, Djokovic, Rafael Nadal and Murray — was drawing inexorably to a close.

"Of course, it hits us top guys hard because we know Andy very well," the world number three said of the three-time Grand Slam champion and double Olympic gold medal winner.

"He's a good guy, Hall of Famer, legend. He won everything he wanted to win. Anybody would substitute their career with his. He's a great guy."

World number one Djokovic played Murray in a practice match three days ago and said it was obvious that there were serious problems.

"You didn't need to be on court to notice that he's struggling, that he's not moving as well as he normally does," said Djokovic, 31, who is just a week younger than Murray.

We've seen so many years of Andy Murray being one of the fittest guys on the tour, running around the court, getting always an extra ball back.

"I think to that extent, we are kind of similar. Our trajectory to the professional tennis world was pretty much similar," added the Serb, who faces American Mitchell Krueger in the first round on Tuesday.

"His birthday is one week before mine. We've grown together playing junior events. We played lots of epic matches.

"Obviously to see him struggle so much and go through so much pain, it's very sad and it hurts me as his longtime friend, colleague, rival.

"I will carry beautiful memories from the court and off the court. It's just sad."

Murray has won Wimbledon twice and Federer hoped the Scot could keep playing long enough to be able to say goodbye on his favourite famous grass courts.

"Of course, I hope that he can play a good Australian Open and he can keep playing beyond that, really finish the way he wants to at Wimbledon," said the 20-time Grand Slam champion, who begins his Australian Open title defence on Monday against Denis Istomin.

"It's a tough one, but one down the road he can look back on and be incredibly proud of everything he has achieved."

Murray was the first British man to win Wimbledon in 77 years and will be remembered for battling his way to world number one in 2016 during a golden era for men's tennis alongside Federer, Djokovic and Nadal.

Murray faces a first-round clash on Monday against in-form Spaniard Roberto Bautista Agut, seeded 22, who beat Djokovic on his way to winning the Qatar Open earlier this month.