Patrick Mouratoglou has said he would happily pay to watch Roger Federer play every day for the rest of his life and considers the 18-time grand slam champion the "biggest legend of tennis".
As the coach of Serena Williams, the 21st century's dominant player on the WTA Tour, Mouratoglou is well aware of what is required to succeed at the highest level.
And the 47-year-old feels he will never again see someone reach the heights Federer has hit during his illustrious career.
Speaking exclusively to Omnisport, Mouratoglou said: "Roger is the greatest player of all time. I don't think anyone has ever played tennis as well as he played, even though he lost to some players and sometimes many times in a row - Rafa [Nadal], for example.
"Nobody plays tennis like Roger. I don't think I will see, before I die, anyone play tennis like him.
"Roger is the same level, even though it's different sports, as Michael Jordan, [Michael] Phelps, Tiger Woods, all those legends. He is the biggest legend of tennis. Plus, it's not over. Maybe in a few weeks, we will talk again and he will have one more grand slam, winning Wimbledon.
"I would sit for hours and I would pay my ticket every day for the rest of my life to watch him play tennis because it's just magic. Nobody plays tennis like this."
Although Federer trails 23-14 in head-to-head meetings with great rival Nadal, the 35-year-old Swiss has won their last four contests, including this year's Australian Open final.
Lauding the tactical changes made by Federer, Mouratoglou added: "He has been smart enough to think the right way and to put on the right strategy to come back to the top of the game. And that's not easy when you've been as dominant as he has been.
"He thought, if I want to win a grand slam again, I have to play five sets against guys who are so fast. They have incredible endurance; they are happy to make the rallies last long and the longer the match, the more I will decline, and if I have to repeat that day after day, I have no chance to win a grand slam.
"So the only chance is to shorten the rallies and I have to modify my game to be able to shorten the rallies in the future. Then I have a good chance to win a grand slam again.
"Hitting his backhand more flat, coming to the net a lot, serving and volleying, all those things made him become who he is now, and I think he really modified his game and since January he brought this new game to the top and he's a different player.
"And now he can beat Rafa, which is incredible, because that's the player who just blocked him so many times from winning many more grand slams. At a certain point everybody thought he will never beat Rafa again, he can't, but he showed that he can with those modifications.
"In the rally, when Rafa hits the high topspin to his backhand, being able to move in, take the ball early and hit flatter [has been key]. As we all know, Rafa doesn't like when the ball comes fast on his forehand. It makes him play short and then you can attack him again. That's how he [Federer] beat him and it's incredible to see him play that level since January."
--- The Coach by Patrick Mouratoglou is now available through Wymer Publishing ---