Rafael Nadal expressed his sadness at Andy Murray's impending retirement but backed the Scot's decision as the right move for his mental health.
A tearful Murray revealed on Friday that the pain in his hip has become too much to bear and the Australian Open could be his final tournament.
Nadal said: "Of course it's very bad news. But when somebody like him, he achieved almost everything in his tennis career, is suffering like he's doing for such a long time already, and you feel that you are not competitive for the thing that really makes you wake up every morning and go on court with the passion to practise, to improve, and with a goal, then it is so difficult.
"Probably he is fighting to keep going since a long time. If he doesn't feel that the thing can go better, probably he does the right thing for his mental health.
"It will be a very important loss for us, for the world of tennis, for the tour, for the fans, even for the rivals that he has been part of a great rivalry between the best players for a long time, and a great competitor. But that's life."
Few people would have put money on Murray being the first of the 'big four' to retire, and his imminent exit is a stark reminder that this golden generation cannot go on forever.
"It seems like he had not a very long career," said Nadal. "But he's 31. Ten years ago, if he retired at 31, we will say he had a great and very long career. We will miss him. But today it's him, tomorrow another one. We are not 20 any more. Our generation, everyone is more than 30."
Nadal was a junior rival of Murray and the pair have known each other for 20 years.
"When he was a kid, he was little bit a bad boy," said the Spaniard with a smile. "I always had a good relationship with him. We shared the court in the most important stadiums in the world, competing for the most important things. That's impossible to forget."
Murray was back on court on Saturday, practising with Grigor Dimitrov on Rod Laver Arena ahead of a first round match against Roberto Bautista Agut on Monday that could be the final act of his glittering career.
Murray has reached the final at Melbourne Park five times but was not given top billing for his potential swansong, with the match taking place on Melbourne Arena, the second biggest court.
It will a strange occasion for Spaniard Bautista Agut, a player known for a gruelling baseline style who is sure to test Murray's hip to the maximum.
He has never taken a set off the Scot in three previous meetings but arrived in Melbourne after beating Novak Djokovic on his way to a ninth ATP Tour singles title in Doha.
He said: "Everybody knows Andy, everybody knows when he goes on court he gives every time 100 per cent. I think Andy's going to fight as he did all his career. It's a great experience for me to play in one of his last grand slams against him so I want to enjoy the experience."
The tributes continued to flow in, including from Tim Henman, the man whose mantle Murray took and then elevated.
The pair are good friends and Henman was saddened but not surprised by the news, telling the BBC: "It has been heading in this direction. I know how hard he has been working and I've been able to speak to him at different times and obviously I'm close to (Murray's coach) Jamie Delgado, too.
"With the amount of work he's been doing, and we know how professional and diligent he is, 20 months is a long time.
"And, obviously, with the nature of the injury, there are a lot of people who have felt this was going to happen at some stage. But it is still so sad to see him so upset before the Australian Open and obviously hearing he is still playing with pain."
Although Murray feels he has unfinished business in tennis, Henman believes he should have no regrets.
"When you look at the list of his achievements, starting with three grand slams, two Olympic golds and finishing world number one, there are no greater goals you can achieve in our sport," said the former world number four.
"He has worked incredibly hard and, having seen that at pretty close quarters, his development from someone who joined us at Davis Cup as a 16-year-old and the way his game has progressed and the way he has matured physically and mentality, it has been incredible to watch.
"I know he will be immensely proud of those achievements even though he will be disappointed at the moment."