Wimbledon champion Marion Bartoli has been forced to pull out of next week's Stanford tournament because of injury.
The Frenchwoman has a strained hamstring and her withdrawal is another blow for the organisers who have already seen Maria Sharapova pull out.
"The injury has not completely healed," Bartoli said of the injury, which she suffered at Wimbledon.
World No 4 Agnieszka Radwanska is the only top 10 player left in the 28-strong field in California, while the only other player in the top 20 is Samantha Stosur.
Bartoli, who has reached the Stanford final three times, has been replaced by American Mallory Burdette, who is ranked 78th.
"It is unfortunate she will not be able to attend," said tournament spokeswoman Kim Hall.
The tournament, which includes both singles and doubles players, runs from July 22-28.