World No.1 Novak Djokovic has dropped out of the Cincinnati tournament with a sore left wrist.
Djokovic was upset at the Olympics in Rio on Sunday, losing to Juan Martin del Potro of Argentina in straight sets.
The top-ranked player informed the Cincinnati tournament that his wrist has been bothering him and needs time to recover.
"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.
"I have played many matches and I have to take some rest in order to heal. I always have my hopes high on returning to Cincinnati and winning the only trophy I am missing in the Masters Series."
He lost to Roger Federer in the finals last year, preventing him from becoming the first to win all nine current ATP Masters events.
Djokovic is 0-5 in Cincinnati championship matches, never winning so much as one set.
By contrast, Federer has won the tournament an unprecedented seven times, going 7-0 in title matches.
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, which overlaps the end of the Olympics. The top-ranked players usually use the Cincinnati tournament as a final tuneup for the US Open, but the Olympics scrambled their schedules this year.
