Roger Federer said on Thursday that Carlos Alcaraz winning the Australian Open to complete the career Grand Slam aged just 22 would be "crazy".
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Spain's Alcaraz already has six major titles but success on the Melbourne Park hard courts is a glaring hole in his resume.
Should the world No 1 snap his Australia drought at the tournament starting on Sunday, he would become the youngest man to seal a career Grand Slam.
"At his young age to be able to complete the career Grand Slam already would be crazy," Swiss legend Federer said at Melbourne Park, where he will headline a "Battle of the World No 1s" at the official launch of the 2026 Australian Open on Saturday.
"Let's see if he's able to do 'crazy' this week. I hope he does because for the game that would be an unbelievable and special moment."
EYEING NADAL RECORD
Alcaraz is aiming to surpass retired compatriot Rafael Nadal, who secured all four majors by the age of 24, but the top seed has not made it past the quarterfinals in four previous Australian Opens.
Federer, a six-time Melbourne champion, compared Alcaraz's wait to lift the title there to Rory McIlroy's agonising attempts to win a first Masters in golf.
The Northern Irishman finally did it last year to complete the Grand Slam.
"It's like Rory going for the Masters. Those things are tough," said Federer.
Alcaraz faces home hope Adam Walton in the first round.
The now-retired Federer was also asked by reporters about Joao Fonseca, an up-and-coming Brazilian tennis talent aged 19.
Federer spoke glowingly of the teenager, saying: "What separates him from a lot of the other guys in the draw is just his power – forehand, backhand, serve and just what he's able to bring point by point.
"He's exciting, he's got good aura, he's a very likeable character as well. I like watching him play.
"The sky's the limit."