Nadal has proved his versatility on all surfaces
Andre Agassi believes Rafael Nadal could achieve the coveted Grand Slam in 2009, 40 years after Rod Laver captured all four major titles in the same year.
Nadal, who has already won the Australian Open this year, begins the defence of the French Open he has won for four years in a row on 24 May.
"This is the first time in a long time we're going to have the opportunity for somebody to pull it off," said Agassi.
"I didn't think I'd ever see it, just because it seems impossible."
Agassi is one of only five men to have won all four Grand Slam titles during their career but his wins came in different years.
"If Nadal retains Paris like he has done for the last number of years and comes to Wimbledon 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," added the now retired Agassi.
I never thought for a second his game could ever translate on grass
Nadal won his first Wimbledon title in 2008 after an epic five-set win over Roger Federer and Agassi pinpointed the Mallorcan's ability to adapt to grass courts as the most impressive part of the development of his game.
"I never thought for a second his game could ever translate on grass but he calls his shots and he executes it.
"The most difficult part of the season would be the transition from clay to grass in two weeks.
"If you ever did well enough in Paris it was a pretty significant challenge to show up at Wimbledon 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."