Swiss world number two Roger Federer could extend his record grand slam tally to 20 if he remains fit and motivated, according to his coach Paul Annacone.
"He can win every tournament he plays, he's probably not going to, but he can win every match he plays and there's not a lot of guys you can say that about," Annacone, a former coach of Pete Sampras and Briton Tim Henman, told the Australian Open website (www.australianopen.com).
"So if he can stay healthy and happy and eager I don't know what the end number would be, but is 20 realistic, sure, why not?"
Defending Australian Open champion Federer hired Annacone after his disappointing quarter-final exit at Wimbledon last year.
He has credited the Californian for helping him mount a late-season resurgence, capped by victory over top-ranked rival Rafa Nadal to win the season-ending World Tour Finals.
Annacone, who works with Swiss coach Severin Luthi in the Federer camp, said he had not joined to teach Federer "how to slice bread" but had helped the Swiss on his strategy and motivation.
"He's not all of a sudden going to have a two-handed backhand," he said. "It's about combining the head, heart and talent components of a player, and understanding how they interact, the best way to match up against other players, and ultimately, the best way for them to keep having fun doing it, and the best way to try to get better.
"If you're not trying to get better you're getting worse, because everyone else is getting better. Roger is very eager to continue improving, so when you see that in someone who's won as much as he has, it's pretty incredible."
Federer, 29, will bid for his 17th grand slam at the Australian Open starting next Monday. He has been in ominous form, kicking off his season with victory at the Qatar Open where he improved with every match and thrashed Russian former top-10 player Nikolay Davydenko in the final.
"His last six months, he's been playing great tennis, had some down time with his family, rebounded last week winning Doha, he's ready to play," said Annacone.
"I don't think I would change much that he's done, his body feels good, his mind feels good, now it's just about getting out there and getting things going."