Roger Federer and Novak Djokovic added their tributes to the outpouring of support for Andy Murray as the Scot gears up for what could be his final professional tennis match.
Murray will face Roberto Bautista Agut in the first round of the Australian Open on Monday before deciding the best next course of action for his injured right hip.
It was a practice match against Djokovic on Thursday that laid bare the seriousness of Murray's continued struggles and led to him emotionally announcing his imminent retirement the following day.
Djokovic did not even appear to be playing quite at full tilt despite losing only two games, but he insisted he was not taking it easy.
"It was very obvious for everyone, you saw it, 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.
"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. His birthday is one week before mine. We've grown together playing junior events. We played lots of epic matches in the professional circuit.
"Obviously to see him struggle so much and go through so much pain, it's very sad and it hurts me as his long-time friend, colleague, rival."
Djokovic posted a tribute on Instagram to a man he has known since they first faced each other as 13-year-olds in 2001, concluding: "Whatever happens, I will always cherish our amazing matches over the years and be grateful for those experiences."
Murray's hip problem first flared up at the French Open in 2017, with the Scot going under the knife the following January.
Late in 2017, Federer took part in Murray's charity exhibition event in Glasgow, and remembers how much the three-time grand slam champion was struggling.
"I know how not well he was," said Federer. "I couldn't believe he actually played. But it was for a good cause.
"I guess everybody can understand where he comes from. At some point when you feel like you're never going to get back to 100%, you've had the success that Andy has had, you can only understand the decision.
"I was disappointed and sad, a little bit shocked, to know now that we're going to lose him 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.
"Of course, it hits us top guys hard because we know Andy very well. We like him. He's a good guy, Hall of Famer, legend. He won everything he wanted to win. Anybody would substitute their career with his.
"It's a tough one, but one day down the road he can look back on and be incredibly proud of everything he has achieved."
Murray has never previously dropped a set against gritty Spaniard Bautista Agut but admitted he is in such bad shape physically that he expects to lose.
As for what comes next, Murray is considering having surgery to resurface his hip. He insisted on Friday that would be for quality of life reasons rather than with a comeback even in the back of his mind, but he has been talking to other players who have had the same procedure.