By Martyn Herman
LONDON (Reuters) - Seven-times grand slam John McEnroe knows how it feels when a tennis career starts going in the wrong direction.
That's why he is paying careful attention to Rafa Nadal's current travails as the Spaniard prepares to try and win a record-extending 10th French Open.
At nearly 29, Nadal is already four years older than McEnroe was when he claimed his last grand slam title.
And after a season in which once rare defeats on his favored claycourts have arrived with alarming frequency, no wonder many believe Nadal has reached a tipping point.
McEnroe, however, thinks it is foolhardy to dismiss the Mallorcan as a fading force and fully expects him to find his 'A game' in the days ahead.
"He obviously wants to try to peak for the French," McEnroe, who will form part of Eurosport's commentary team at the championships, told Reuters by telephone on Thursday.
"He was out for a while, he came back, he figured he would work his way back to the sort of level he needs and the confidence level he needs to win again.
"I guess by Madrid or Rome he would at least liked to have won one or two but it's hard not to think that he's gonna take it up to another level (at the French) unless there's physically something wrong with him."
Former world number one McEnroe says everything points to Novak Djokovic winning his first French Open and says the only player capable of stopping the in-form Serb is Nadal.
"It's hard to think that there's anyone who could beat Novak other than (Nadal) in a five set match based on what I've seen," said McEnroe, who let slip a two-set lead against Ivan Lendl in the 1984 French Open final and was never the same again.
While McEnroe's career decline was triggered by the early retirement of great rival Bjorn Borg at 25, Nadal, according to McEnroe, is suffering the consequences of his physical style.
Where Pete Sampras used to serve players off court, 17-times grand slam champion Roger Federer dazzles and Djokovic clinically dissects them, Nadal's magnificent career has been built on warrior-like instincts.
"He's had such an unbelievable record but he's a human being and at some point it tails off to some degree," the 56-year-old said.
"It's hard to pinpoint when exactly that will happen but he doesn't seem like he's himself.
"Maybe on the clay where you have to grind more than on other surfaces, you can get exposed a little sooner and people start wondering what's going on.
"There's always a moment in a players' career when it starts to go in the wrong direction or they stop playing altogether."
"He's put a lot of miles on the body, and mentally the way he operates and the energy he uses emotionally and physically, given his style of play, it takes it's toll.
"He's the type of guy that likes matches but he's also the type of guy that needs more rest so that's a difficult line to find that right mix at this point."
While all eyes will be on Nadal and Djokovic, McEnroe said Andy Murray and Japan's Kei Nishikori are the two most likely players to spring a surprise.
"Murray has always had the game to do well at the French and he's made a couple of semis and right now is playing with the most confidence I've ever seen him on clay," he said.
"And Nishikori beat Novak at the U.S. Open in extreme heat, he did an unbelievable job and it's conceivable he could do that again."