Bulgarian Tsvetana Pironkova was beating the third-seeded Li 7-6 (7-5), 3-2 when the Chinese star quit with a sore back.
"It was so painful," Li said. "That's why I called the physio to come to the court. I tried to tape and then tried to play the point, but it didn't work. I'll go to the hospital to take an MRI to see what happened."
Additional opening-round wins came for Czech Petra Cetkovska, Croat Petra Martic, South African Chanelle Scheepers, and Germans Angelique Kerber and qualifier Mona Barthel, who captured her first-ever WTA title in Hobart last month. Barthel bested Czech Barbora Zahlavova Strycova 6-3, 6-2 Tuesday in Paris.
The top seeds here are Australian Open and Wimbledon runner-up Maria Sharapova and former Wimbledon finalist Marion Bartoli, both of whom received opening-round byes. The three-time major champion and former world No. 1 Sharapova will open her week against Scheepers on Wednesday, while Bartoli will take on Martic on Thursday.
The winner of this $637,000 event will pocket $107,000.