Stan Wawrinka has withdrawn from Madrid, joined by Jo-Wilfried Tsonga who will also not play Rome.
Wawrinka, who recently reunited with coach Magnus Norman, had double knee surgery in 2017 and has been on another break since returning at the beginning of the season. But the former French Open champion has resumed training and says he still plans to play during the clay-court season.
Tsonga, who underwent a small procedure on his knee just a few weeks ago, now looks doubtful for the French Open but says that he is working towards a return.
TC Live discusses Wawrinka's decision to withdraw from Indian Wells and Miami:
"I am not 100 percent, I cannot move as I would like. But I am on the courts again," the Frenchman was quoted as saying by AFP.
The tournament will also not have Roger Federer, who is not playing the clay events, and Andy Murray, who is still sidelined following hip surgery.
Nick Kyrgios and Sam Querrey are among the other players who have withdrawn from the Masters tournament.
Rafael Nadal will be the defending champion and top seed.