Already missing several top players from this year's lineup, the Bank of the West tennis tournament received more bad news Thursday when Serena Williams withdrew due to a lingering thumb injury.

World No. 5 Ana Ivanovic of Serbia, who would've been the tournament's top seed, withdrew last month after reaching the finals of the French Open. Then 20th-ranked Na Li withdrew on July 2. Now Williams, who's No. 7 in the world, is also gone one day before the Stanford tournament's draw takes place.

The top seed will now be Russia's Anna Chakvetadze, No. 8 in the world. Marion Bartoli of France, who rose to No. 11 after making the finals at Wimbledon, is the next highest ranked player.

Other top 20 players still in the mix include Daniela Hantuchova (No. 12), Patty Schnyder (16), Shahar Peer (18) and Tatiana Golovin (19).

In 2003, Williams withdrew from the tournament, citing a knee injury.