"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.
Novak Djokovic insisted Sunday no decision had been taken about ousting ATP Tour chief Chris Kermode after reports of a player revolt against the way the sport was being run.
Murray's announcement brings down the curtain on a career in which he became the first British man to win a Wimbledon singles title in 77 years, despite an early life marked by tragedy.
But Dr John O'Donnell, who operated on the Scot's troublesome right hip, said: "I don't think it is impossible, but it will be very hard".
Top seed Djokovic, who launches his campaign for a record seventh crown against American Mitchell Krueger on Tuesday, said he also enjoyed strong support from Melbourne's large Serb community. His birthday is one week before mine.
"Tennis will come to an end for us all but the friendships will last a lifetime", tweeted tennis player Grigor Dimitrov".
"I feel like time has gone insane fast since I won here". However, she has reached two grand slam finals since returning from giving birth and the seven-times Australian Open champion will be raring to go after missing last year's tournament.
"I can still play to a level - not a level I'm happy playing at", he said. But it was for a good cause.
"Of course, she's not number one in the world, and I have a lot of respect for the number one but I still feel that if Serena plays her tennis and she's herself 100 per cent, I still think she's the best".
"But we're going to lose everybody at some point".
"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", Federer said.
"His record is phenomenal and he did it all not only with humility and good grace, but also with a dry sense of humour that marks him out as a true Scot". "Obviously it was something that I really wanted, a big dream of mine to win a grand slam, and it was an unbelievable feeling and an incredible two weeks". Anybody would substitute their career with his.
Williams has a tough road to an eighth title, with world number one and French Open champion Simona Halep a potential quarter-final opponent followed by Osaka in the semi-finals if the seeds hold sway.
The quality may not be the best, but it will be fascinating to see Murray push through the pain in a final bid to get a win at a tournament he's been a runner-up at on five occsions.
"But nothing new for me". It's going to be uncomfortable. The answer to your question is: I do not see them winning it. I think maybe it showed a little bit at the Hopman Cup already. "I'm just taking it as a nice, fun challenge", the third-seeded Wozniacki said. I had a couple of (times) of this. I really appreciate what he's done for women's tennis. "I know what Denis did to Novak".