Former world number one Pete Sampras says he cannot see anyone in the game capable of challenging the supremacy of current number one Roger Federer.
Federer has dominated the game since Sampras retired
Since Sampras retired four years ago, the 24-year-old Swiss player has won seven Grand Slams and been world number one for two years.
"I don't see anyone with a big enough weapon to hurt him," said Sampras.
"They're just staying back and Roger is able to dictate well enough. You just have to serve well and attack him."
Sampras, 34, retired in 2002 after winning a record 14th Grand Slam title, and has spent much of the intervening period playing golf and poker.
Having scarcely picked up a racket for three years, he will play Robby Ginepri in an exhibition match in Houston on Thursday and aims to play World Team Tennis, but insisted a tour comeback is not on the cards.
"When you retire you want to get as far away as possible from the game for a few years," he said.
"I'm just getting in shape and having some fun. I've been hitting some balls for the past month. Hopefully I won't embarrass myself."