The former tennis world number one Ana Ivanovic was the latest high-profile player to exit the China Open when the Serb retired from her quarter-final against Agnieszka Radwanska with back problems.
The 23-year-old was a set down when the injury she sustained last week in Tokyo flared up in the second set.
Maria Sharapova and Serena Williams pulled out of the competition a week ago, Victoria Azarenka failed to show for her match on Thursday due to injury while home hope Li Na exited in the first round, Sam Stosur went out in the second and Vera Zvonareva the third.
In the men's draw, world No. 1 and 2010 champion Novak Djokovic was forced to pull out because of a back injury.
Romanian Monica Niculescu came from behind to beat Maria Kirilenko 3-6 6-3 6-4 to clinch a semi-final berth while in the men's competition Tomas Berdych thrashed Spaniard Fernando Verdasco 6-1 6-0 to seal a place in the last four.
