CINCINNATI (AP) Top-seeded Serena Williams has withdrawn from the Western & Southern Open with a shoulder injury, the tournament announced on Monday.
Williams, the tournament's two-time defending champion, withdrew on Monday after a morning practice session, according to tournament officials.
She accepted a wild-card berth in the tournament last week after being upset in the third round of the Rio Olympics.
The withdrawal gives second-seeded Angelique Kerber an opportunity to earn the WTA No. 1 ranking if she were to win the W&S title.
Williams has been ranked No. 1 for 183 consecutive weeks and 306 overall.
Japan's Misaki Doi replaces Williams in the draw, receiving Williams' first-round bye.