Serena Williams has been forced to pull of the US Open women's doubles because of injury.

The 18-year-old American, who won the title last year with elder sister Venus, has an inflamed big toe of her left foot.

The Williams sisters were due to play Zimbabwe's Cara Black and Russia's Elena Likhovtseva in the semi-finals.

The withdrawal caps an unhappy couple of days for Serena, whose defence of the women's singles title was ended by fellow American Lindsay Davenport in the quarter-finals.