Dominic Thiem has withdrawn from the Monte Carlo Masters, saying he is not yet ready to return to competition.
The 27-year-old Austrian, who also withdrew from this week's Masters tournament in Miami, has not played since his opening-round loss to Lloyd Harris in Dubai.
"I had to take a break. I'm not 100 percent ready yet," Thiem said on his official website, adding that he would be returning to training. "I have a lot to work on."
Thiem has been bothered by a foot injury, but according to his agent, Herwig Straka, that was not why he decided not to play.
"Domi is not injured," Straka told Kleine Zeitung. "He just wants to give himself more preparation time."
Straka, who had previously also said that Thiem found competing in a tournament 'bubble' difficult, added that he had never had a lot of success in Monte Carlo, but planned to play regularly before Roland Garros.
"As things stand, [Thiem] will start the clay-court season with Belgrade," said Straka. "This will be followed by the Masters events in Madrid and Rome."
John Isner and an injured Borna Coric also withdrew from Monte Carlo.
Djokovic is scheduled to play Monte Carlo, followed by his hometown event in Belgrade, which is being played in his tennis center. He will then have two weeks off before playing Rome. But he has not officially withdrawn from Madrid or confirmed that he is not playing.
Thiem is No. 4 in the rankings, while Djokovic is the world No. 1.
Monte Carlo will be the first tour event to offer testing exemptions for vaccinated players.