British number one Andy Murray can transfer his world-class form from hard courts to clay, according to three-time Wimbledon champion John McEnroe.
Murray pulled out of a doubles match in Monte Carlo
Murray has rocketed into the world's top 10 with superb results on grass and hard courts over the last year.
But he won only four matches on clay in 2006 and a back injury means he has yet to complete a match on clay in 2007.
"This is his most vulnerable surface but I think he can be successful," said McEnroe, a former French Open finalist.
Murray hopes to be back in action at next week's Masters Series event in Rome.
"It's going to be tough for him initially," McEnroe told the BlackRock Tennis Champions Podcast.
It is quite clear that Nadal is the man to beat and Roger is going to have to do something different
"His fitness levels have improved and he's got some good variety, and he grew up playing on clay.
"However, there's a lot guys out there that think they have a better chance against him on clay. He can't change pace as easily and hurt people as much as he would like.
"I think he can win two, three, four rounds at the French. He certainly won't be easy to beat and he is capable of getting to the round of 16 or the quarters.
"He needs to get out there, play some matches and get some confidence."
Rafael Nadal remains the man to beat on clay having stretched his unbeaten run to 72 matches and beaten Roger Federer in the recent Monte Carlo Masters final.
"I think [Federer] has fallen for playing his opponent's game - getting a little tentative and playing way behind the baseline," said McEnroe.
"I think he should step it up and put some pressure on Nadal, make him hit passing shots on the big ones.
"I think he should go back to the drawing board with his coach Tony [Roche] and shorten some of the points, really attack him.
"I'm not saying do it on every point, but he needs to give Nadal a different 'look'.
"Any guy that is as good as Federer I can see figuring it out, but it is quite clear that Nadal is the man to beat and Roger is going to have to do something different to beat Rafael - go back to the drawing board, go to plan B."