Serena Williams withdraws from Cincinnati

World number one Serena Williams has pulled out of the WTA Western and Southern Open due to injury.

Defending champion Williams, 34, was forced to withdraw from the Cincinnati tournament due to a shoulder complaint.

Her exit means both the top ranked man and woman in the world have pulled out after poor Olympic campaigns, with Novak Djokovic also withdrawing from the ATP event.

"I'm very disappointed I'm not able to compete, as I was really looking forward to defending my title," Williams said.

"My shoulder inflammation continues to be a challenge, but I am anxious to return to the court as soon as possible."

Williams has been replaced by Misaki Doi of Japan.