Defending champion Rafael Nadal remains a doubt for the French Open after pulling out of next week's Monte Carlo Masters with an ongoing hip injury.

The 36-year-old has not played since his straight-set second-round defeat by American Mackenzie McDonald at the Australian Open in January.

World number two Carlos Alcaraz is also out of Monte Carlo through injury.

The Spaniard, who is chasing Novak Djokovic for the number one ranking, has hand and back problems.

"After two months abroad I am happy to return home, but sad because I finished my last match in Miami with physical discomfort," said Alcaraz, who lost to Jannik Sinner in the last four of the Miami Open, on Twitter.

"I will not be able to go to Monte Carlo to start the clay-court tour. I have post-traumatic arthritis in my left hand and muscular discomfort in the spine that needs rest to prepare for everything that is to come."

Nadal had expected to be out for six to eight weeks after an MRI scan following his Melbourne loss showed a tear in his left psoas muscle.

But missing the start of the European clay-court season leaves him short of match practice before the Roland Garros event he has won a record 14 times, which begins on 28 May.

"I'm still not ready to compete at the highest level," Nadal said on Twitter.

"I will not be able to play in one of the most important tournaments of my career, Monte Carlo.

"I am not yet in a position to play with the maximum guarantees and I continue my preparation process, hoping to return soon."

Canada's world number seven Felix Auger-Aliassime will also miss next week's event with a left knee issue, but has said he hopes to be back for the Madrid Open which starts on 26 April.