French Open champion Li Na retired injured from her first-round match against Bulgarian Tsvetana Pironkova at the Paris Open on Tuesday.
China's Li, the world number nine, threw in the towel when she was 7-6 3-2 down. The third seed had called on the trainer earlier to treat back pain.
Also on Tuesday, former world number one Jelena Jankovic of Serbia pulled out with a thigh strain.
The World No 13, seeded fourth in Paris, picked up the injury in a Fed Cup tie against Belgium last weekend.
"I am really disappointed not to play here," she told a news conference. "I don't know when I will be able to resume playing but I don't regret having played in the Fed Cup."
