World No 2 Maria Sharapova has pulled out of next week's Bank of the West Classic at Stanford due to the left hip injury she suffered at Wimbledon.
The four-time Grand Slam winner suffered a surprise second round exit at the grass course Grand Slam recently, losing 3-6 4-6 to Michelle Larcher de Brito.
The Russian fell over several times during the match and took a medical time-out, saying later she thought she might have sprained a hip muscle.
Stanford tournament director Kim Hall said in a statement that organisers "are disappointed for our fans" but that "unfortunately injuries are a part of the sport and we understand that a player's health must always come first".
Hall added that Belgium's Kirsten Flipkens, a semi-finalist at Wimbledon, had pulled out of the event as well.
Sharapova and Flipkens will be replaced in the 28-player draw by World No 46 Daniela Hantuchova and Christina McHale, who is ranked 79th.
Sharapova has just announced the hiring of Jimmy Connors as her new coach, having parted company with Thomas Hogstedt.