Novak Djokovic has pulled out of next week's Madrid Open, organisers said on Saturday, with the world number one joining Rafa Nadal on the sidelines.

Djokovic, who was unable to play in the U.S. hardcourt swing earlier this year because he has not been vaccinated against COVID, was preparing for the clay season but got knocked out early at the Monte Carlo Masters and Banja Luka Open.

"I didn't feel well on the court, my legs were slow and my footwork was torpid, many missed shots, totally without direction," said the 35-year-old Serb after his quarter-final defeat by Dusan Lajovic at the Banja Luka event.

Djokovic said, however, that he was still hopeful of finding his groove on clay before next month's French Open.

"Wishing you a speedy recovery, we hope to see you back on court as soon as possible, Nole," organisers said in a statement without giving any details on Djokovic's condition.

Nadal announced earlier this week that he would miss the Madrid tournament after a setback in his recovery from a hip injury sustained at the Australian Open in January.

The two players share the record for most Grand Slam titles, with 22 each. The French Open, the second Grand Slam of the season, begins on May 28.