Novak Djokovic has dropped out of the Cincinnati tournament with a sore left wrist, costing the Masters event another top player.

Djokovic was upset at the Olympics in Rio on Sunday, losing to Juan Martin del Potro of Argentina in straight sets. He informed the Cincinnati tournament on Wednesday that his wrist has been bothering him and needs time to recover.

The Cincinnati tournament is the only Masters event he has yet to win. He lost to Roger Federer in the finals last year.

Federer also will miss the tournament, taking the rest of the year off to build up a surgically repaired knee.

Serena Williams, the defending champion on the women's side, also plans to skip the tournament.