Top-ranked men's tennis star Novak Djokovic said he was "shocked" to hear the news about Andy Murray announcing his retirement on Friday.
An injury-wrecked Murray has conceded that the season-opening major at Melbourne Park starting on Monday could be his last before he retires.
Few could relate to the Scotsman's devastation like Djokovic, who faced his own tennis mortality early last year after battling a severe elbow injury.
Born a week apart and having risen through the junior ranks together, the pair have battled through seven grand slam deciders including Murray's epic victory at Flushing Meadows in 2012 to break through at a major for the first time.
But while Murray's hip issues have him preparing for an inevitable end, Djokovic has bounced back from his own injury crisis to take out last year's Wimbledon and US Open crowns and eye off a record seventh Australian Open title.
"It's quite a shock for me honestly because we are the same age, the same generation," Djokovic said at a sponsor's event in Melbourne.
"It's quite sad to see him going through what he has been going through ... as someone who has been through a major injury with my elbow in the last couple of years, I can definitely empathise with him and relate to what he's going through.
"I trained with him a couple of days ago and we got to chatting a little bit. He's a great champion, he's a friend of mine that I grew up with.
"It's kind of sad to know that he might play his last Australian Open but I do wish him all the best. There's a lot of things in life I'm sure to be grateful for."
Kyle Edmund, British men's number one, said his compatriot "may be Britain's greatest ever sportsman".
"For me he's been my biggest role model out of any tennis player," said Edmund, who first met Murray when he was 14 and started hitting with him a few years later.
"To be able to have had the experiences that I've had with him and memories of training with him and getting to know him personally, and seeing what he's done on the court and achieved, he's definitely helped my career."
British women's number one Johanna Konta said she could "not imagine the sport without him", while Heather Watson said he "can't be replaced" in British tennis.
Billie Jean King added her tribute, writing on Twitter: "You are a champion on and off the court. So sorry you cannot retire on your own terms, but remember to look to the future. Your greatest impact on the world may be yet to come. Your voice for equality will inspire future generations. Much love to you and your family."
Juan Martin Del Potro, who can empathise more than most with Murray's injury struggles, urged the Scot not to give up.
He wrote on Twitter: "Andy, just watched your conference. Please don't stop trying. Keep fighting. I can imagine your pain and sadness. I hope you can overcome this. You deserve to retire on your own terms, whenever that happens. We love you and we want to see you happy and doing well."