Spaniard is 'mortal' on clay again - Jim Courier

Jim Courier has backed Serena Williams and Novak Djokovic to claim the second legs of respective potential Grand Slams at the French Open, with the latter expected to capitalise on Rafael Nadal's poor form.

Nadal will arrive at Roland Garros this year without a lead-up clay court title for the first time since 2004, after his quarter-final exit at the Internazionali d'Italia last week.

While Courier insists five-set matches in Paris will suit Nadal, the American ex-pro claims the Spanish nine-time French Open champion has a target on his back.

"For the first time in many years Nadal will not be the favourite going into Roland Garros. That role is now firmly occupied by Novak Djokovic," Courier - a two-time French Open winner, who works as a tennis pundit - told ITV.

"Nadal is less vulnerable in Paris, given the best of five set format which allows him time to problem solve, than he has been elsewhere but there are now guys in the locker room who see him as an opportunity rather than an immovable obstacle."

Nadal's struggles have seen Courier back the world's leading male and female players to triumph at the French major.

"Given they are both heavy favourites, I am most looking forward to seeing if Serena and Novak can each claim the second leg of the Grand Slam," he said.

Courier also believes two of the younger players on the ATP Tour could prove difficult opponents at Roland Garros: "Kei Nishikori is my second favourite in Paris behind Djokovic and I firmly believe he is the second best clay court player today.

"Also, Nick Krygios has the game, aggressive energy and athletic ability to stir things up the way he did at Wimbledon last year and in Australia in January."

The French Open begins on Sunday.