Roger Federer’s impact on tennis is a lot like the influence Michael Jackson had on pop music, according to Andre Agassi.

The former world No. 1 made the comparison while speaking to Business Insider’s Alan Dawson at Wimbledon, saying that fans who have not seen Federer play in person will regret it once he’s retired.

“It’s going to be like the person that says, ‘I never saw Michael Jackson perform,'” Agassi said. “I can imagine a lot of people saying, ‘I can’t believe I never saw him play.’ He’s left that kind of mark on the game. He’s changed it.

“It will be a sad day (when Federer retires). But it will also be a glorious one because I know what he deserves now for the rest of his life, he deserves to feel something he’s never felt before and I know life will offer (that to) him.”

Federer turns 37 next month and has acknowledged “the end is closer than ever before.” Still, Agassi believes he has plenty left in the tank.

“Roger is still setting a level that is still pretty remarkable,” he said.