London - Andre Agassi has tipped Rafael Nadal to surpass his own achievements and win a calendar grand slam.
Nadal, who begins the defence of his French Open title later this month, is undefeated at Roland Garros since 2005 and, after adding the 2008 Wimbledon and 2009 Australian crowns to his collection, the world number one has proved his versatility on all surfaces.
Agassi, who was at Wimbledon on Saturday, believes the Spaniard could become the first man since Rod Laver in 1969 to complete a rare Grand Slam.
"When he first won in Paris and he came here and said it was awesome to win the French Open but his dream was to win in Wimbledon, people laughed and I was one of them," the American told reporters a day before playing in an exhibition event to unveil the new roof over Wimbledon's Centre Court.
"I never thought for a second his game could ever translate (on grass) but he calls his shot and he executes it and it wouldn't shock me to see him pull off the unthinkable.
"The most difficult part of the season would be the transition from clay to grass in that sort of time frame (two weeks).
"If you ever did well enough in Paris it was a pretty significant challenge to show up here feeling ready physically, emotionally or mentally.
"So to see what Nadal managed to accomplish last year was part of what made it so special, watching that epic final (win over Roger Federer in five sets) that probably transcends any other match ever played."
The now-retired Agassi is one of only five men to have won all four majors during their career but his wins came in different years.
"I didn't think I'd ever see it (a calendar grand slam) just because it seems like the impossible (but)... this is the first time in a real long time we're going to have an opportunity to see somebody maybe pull that off."
For years, Federer had been the man everyone thought would follow in Laver's footsteps. But despite winning 13 grand slam titles, one short of Pete Sampras's overall record, the Swiss has yet to conquer Roland Garros.
Nadal has wrecked Federer's Parisian dreams for the past three years and the signs are that the 22-year-old is again primed to flatten all those who dare to face him on red dirt.
"With Federer we got to the French Open and his chances (of a calendar grand slam) ended there because of Nadal in the last few years. If it hadn't been for the freak from Mallorca, Federer would have won all the slams a few times," said Agassi.
"If Nadal retains Paris like he has done for the last number of years and comes here with the confidence to put together two good weeks, I think we could be looking at him in New York with a realistic opportunity of going on to achieve the unthinkable."
The French Open begins on May 24.