Injury blow for Williams

World number one Serena Williams has withdrawn from the Acura Classic in San Diego, California due to a recurring knee injury.

Williams has experienced pain in her left knee throughout the year, and was troubled with it again last week when she withdrew from the Bank of the West Classic in Stanford.

Her next scheduled event is the JP Morgan Chase Open in Carson, California which starts on August 4.

Lucky Loser Meilen Tu replaces Williams in the Acura Classic draw.