China's Peng Shuai pulled out of the Cincinnati Tennis Open shortly before she was due to face Serbia's Jelena Jankovic in their quarter-final match.
Peng withdrew because of a left hip injury, giving Jankovic a walkover into tomorrow's semi-final against German Andrea Petkovic.
The other semi-final is an all-Russian affair between Maria Sharapova and Vera Zvonareva.