ROME (AP) Serena Williams has withdrawn from the Italian Open ahead of her second-round match against sister Venus due to an old left knee injury.

Tournament organizers made the announcement on Tuesday, a day after Serena opened her clay-court season with a straight-sets win over Swedish qualifier Rebecca Peterson.

It's the third straight tournament the 37-year-old Serena has exited from due to physical problems.

She retired due to a viral illness during her third-round match against Garbine Muguruza in Indian Wells, California, and withdrew with a left knee injury before her third-round match at the Miami Open in March.

As a result of this latest withdrawal, Venus advances into the third round via a walkover.

It wasn't immediately clear if Serena would recover in time to play the French Open, which starts in less than two weeks.

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