STANFORD, Calif. - World No. 1 Serena Williams has withdrawn from the upcoming Bank of the West Classic because of an elbow injury she says must get "back to 100 per cent."

The tournament announced her withdrawal Friday. It runs Aug. 3-9 at Stanford University.

Williams expressed her disappointment and noted, "The tournament is one of my favourites and the fans have always been so generous and supportive of me."

Williams recently won her sixth Wimbledon championship, 21st Grand Slam singles title overall and fourth consecutive major event — the "Serena Slam" — and she also won four Slam events in a row in 2002-03. She will now look to chase a fifth straight at the U.S. Open in August.

Williams is currently scheduled to play at the Rogers Cup in Toronto, which starts next week.

Fifth-ranked Caroline Wozniacki will make her Bank of the West Classic debut, and as the top seed.