At Melbourne Park in his dual role advising six-time champion Novak Djokovic and as a global ambassador for Lavazza, Agassi's career ended rather abruptly after the former world No 1 failed to regain full fitness after spraining an ankle.
The American considers Federer a different beast. "We all know what Federer has done and can do, but I've never sort of lived with Federer so you don't have a full appreciation of what his capacity level is," he said.
"He manages himself really well. He makes a lot of great decisions.
"The only thing I can say in full confidence is that when the end comes, it does come quick.
"But that doesn't mean he's at the end. He's obviously made some very calculated, smart decisions to get his body to what it needs to be to be able to keep doing this.
"So it wouldn't surprise me for him to be around for a while longer."
In his 20th year on tour, Federer is half hoping his children don't follow his path after revealing his 8-year-old twin daughters had "fallen in love with tennis".
"I hope they don't just because we don't need another 25 years on tour," he said.
"No, I'm just a supportive parent. I can't tell which direction they're going to go, if there's going to be anything in sports or somewhere in finance or business. I have no idea.
"All I know is I'll be incredibly supportive of them. It's great for them to do sports early on in their life. I think it's good for them."
