Serena pulls out of Athens Games

Serena Williams has withdrawn from the USA Olympic tennis team.

Williams has been struggling recently with a knee injury which forced to pull out of tournaments in San Diego and Montreal, but it has not yet been revealed why she has decided against competing in Athens.

She had been hoping to add another gold medal to her collection, having triumphed with sister Venus in the women's doubles four years ago.

She was also entered to play doubles with Venus this year, and it is not known whether another member of the US squad will now partner Venus.

Chanda Rubin or Lindsay Davenport could take Serena's place.

The former world number one's place in the draw will be taken by Australian Samantha Stosur.