LONDON (Reuters) - Novak Djokovic may never have a better chance to complete his career grand slam than at this year's French Open but those predicting the decline of claycourt king Rafa Nadal should be wary, according to Andre Agassi.
Had it not been for the Spaniard, Djokovic would already be part of the elite club of players to have won all four majors -- one that Agassi joined when he finally prevailed in the French capital in 1999 against Andriy Medvedev.
Twice Djokovic has been felled by Nadal in the final while in 2013 he lost an epic five-set semi-final.
World number one Djokovic's dominant start to the year and Nadal's sluggish return from more injury woes means that the odds are shortening on him ending the Spaniard's dominance on the red dirt which has earned him a record nine titles in 10 years.
"Rafa has been the Mount Everest of Roland Garros and climbing him is like climbing Mount Everest without the sherpas and the oxygen," Agassi told Reuters TV at the launch of his BILT by Agassi & Reyes range of fitness machines at a sports club just north of London this week.
"Djokovic has nearly reached the summit of that mountain a couple of times and is no doubt playing at a level above everybody else right now.
"He believes he should win. I think he can and deserves to but he doesn't deserve it if Rafa gets himself right and shows up again like he has. I will be as excited as anybody to see if Rafa really is going to be vulnerable. It seems that way now but it's seemed like that before."
Agassi, 44, hung on long enough to watch the emergence of Nadal, who he describes at the most physically intimidating player he faced in a career that reaped eight grand slam titles.
Nadal won both their meetings, the last at Wimbledon in 2006, shortly before the American great retired.
He suggested that Nadal's brutality had broken new ground in the sport, ushering in an era of super-athletes.
"You could give them all wood rackets and these guys are still bigger and stronger and faster," Agassi said.
"You add the spins, you add the speed. You add the rules of engagement. The points are more ballistic then they've ever been and they go longer than they've ever gone.
"These guys are playing to depletion. I mean, my word! It's violent. Sprinting five miles in a match, there's no jogging. I mean I played with urgency because I needed to raise the stakes and get to someone physically, these guys do it for five hours."
Nadal's back and wrist problems last year, added to the wear and tear on his creaky knees, has prompted suggestions that, at 28, his body is no longer capable of producing the sustained level of intensity that left most of his rivals reeling.
He complained of tiredness when losing on clay to flashy Italian Fabio Fognini in Rio de Janeiro this month while at the Australian Open he was annihilated by Czech Tomas Berdych who had lost their previous 17 meetings.
"His form will come around if he's healthy but the question is do I have the confidence that he hasn't pushed his body too far? I don't have that confidence because he's the most physical player I've ever seen," added Agassi.
"You've got to pay the piper at some point, your body can't do it for ever."
Reporting by Martyn Herman, editing by Pritha Sarkar