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  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.
  Djokovic has pulled out of the Cincinnati Masters, which starts on 14 August.
  "I am very sad to announce that I won't be able to play this year in Cincinnati," he said.
  "I have a recurring injury that has taken its toll on my body due to a very busy and active schedule this year.
  "I have played many matches and I have to take some rest in order to heal."
summary: World number one Novak Djokovic says a recurring wrist injury has "taken its toll" after a "very busy and active" year.