World number one Novak Djokovic has withdrawn from the Cincinnati Masters because of a wrist injury.
The Serb, 29, was knocked out in the first round of the Rio Olympics tennis tournament by Juan Martin del Potro.
He also suffered a surprise defeat by Sam Querrey in the third round of this year's Wimbledon.
"I have a recurring injury that has taken its toll on my body due to a very busy and active schedule this year," Djokovic said.