Nadal has been dominant on clay in recent yearsDefending 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 Spanish world number 14 has won the tournament in Monaco 11 times but is not fit to return to action.
The 36-year-old has not played since losing to American Mackenzie McDonald in straight sets in the Australian Open second round in January.
"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."
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 Nadal short of match practice before the Roland Garros event he has won a record 14 times, which begins on 28 May.
