French Open champion Li Na of China and Serbia's Jelena Jankovic were both forced to withdraw from the WTA Paris Indoor Open on Tuesday because of injuries.
Third-seeded Li withdrew while trailing Bulgarian Tsvetana Pironkova 7-6 (7/5), 3-2 in their first round tie at the Paris-Coubertin Stadium.
Li was visibly suffering with a back problem and finally called it a day after receiving treatment courtside.
Earlier world number 13 Jankovic, the fourth seed, withdrew after failing to recover from a left thigh injury she picked up during her win over Belgium Kirsten Flipkens in Serbia's Fed Cup World Group first round success last weekend.
"I had hoped that after treatment I could still play here but unfortunately it's impossible," said Jankovic.
Germany's Mona Barthel advanced to the second round after beating Barbora Zahlavova Strycova of the Czech Republic 6-3, 6-2 with another Czech Petra Cetkovska advancing past Italy's Alberta Brianti 6-3, 6-3.