Rafael Nadal says he is in a “difficult” situation as he does not know when he will return from his injury lay-off.
He was initially ruled out for six to eight weeks with a hip injury but has now not played since 18 January.
Nadal confirmed he will miss the Madrid Open, which starts on 25 April, and there is doubt over his participation at the French Open in May.
“The injury still hasn’t healed,” the 36-year-old Spaniard said.
“I can’t work out what I need to compete. I was training, but now a few days ago we decided to change course a bit, do another treatment and see if things improve to try to get to what comes next,” he explained in a video posted on his social media channels.
“I can’t give deadlines because if I knew I would tell you but I don’t know. This is how things are now.”
Nadal, who won his 14th French Open title last year, was diagnosed with a tear in his left psoas muscle after losing in the second round of the Australian Open in January.
The 22-time Grand Slam winner added: “I have no choice but to try to have the right attitude throughout this time, try to give myself the opportunity to compete in one of the tournaments that remains of the clay season and I have no choice but to work and be with the right mentality.”
The French Open starts on 28 May.
Meanwhile, Olympic champion Belinda Bencic says she will miss both Madrid and Rome’s clay tournaments because of “discomfort” in her hip.
The Swiss said she was struggling with the injury throughout the WTA Tour’s United States swing, despite still making the Charleston Open final.
Bencic said she has taken the decision to help her be 100% fit for Roland Garros.