World number one and defending champion Serena Williams withdrew Friday from next week`s WTA hardcourt tournament in Stanford with a right elbow injury, organizers said.
"I`m disappointed to have to withdraw from the Bank of the West Classic, but I need to get my elbow back to 100 percent," Williams said in a statement released by tournament officials.
"The tournament is one of my favorites and the fans have always been so generous and supportive of me. I wish all of the players much success and I hope to return next year."
The 33-year-old American had planned to start her buildup to the US Open in Stanford.
She`s coming off a Wimbledon triumph that marked her fourth straight Grand Slam victory -- and which gives her a shot at completing an elusive calendar Grand Slam.
It`s the second planned start since Wimbledon that Williams has skipped because of her right elbow.
She was forced out of the Swedish Open earlier this month.
Williams next scheduled US Open warm-up is at the hardcourt tournament in Toronto in two weeks.
"Serena is having a historic season and we wish her a speedy recovery as she prepares for the US Open," said Stanford tournament director Vickie Gunnarsson.
"Unfortunately injuries are part of sports and the health of the players is always the number one priority."
In Williams` absence, Denmark`s Caroline Wozniacki will be the top seed.