Stan Wawrinka will not defend his US Open title and will miss the rest of the season after deciding he required a knee operation.
The 32-year-old was troubled by a left knee problem during a first-round loss to Daniil Medvedev at Wimbledon and revealed earlier this week he would miss the Masters events in Montreal and Cincinnati.
But Wawrinka has since made the decision to take direct action in a bid to cure the problem.
"I am sad to announce that, after talking with my team and doctor, I had to make a difficult decision to undergo a medical intervention on my knee," he said in a statement released by his management.
"This was the only solution to make sure I will be able to compete at the top level for many more years."
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Wawrinka won his third grand slam title in New York with victory over Novak Djokovic last September.
Neither will be at Flushing Meadows this year, with Djokovic also calling an early end to his season to rest an elbow problem that forced him to retire during his Wimbledon quarter-final against Tomas Berdych.
It remains to be seen, meanwhile, whether world No.1 Andy Murray will be fit enough to compete as he continues his recovery from a hip problem.
Murray has withdrawn from next week's Rogers Cup in Montreal but has not yet announced whether he will play in Cincinnati the following week or at the US Open.
Continuing his statement, Wawrinka said: "This is obviously extremely disappointing, but I'm already looking ahead and planning my recovery.
"I love this sport and I will work hard to get back to my top level and play many more years."
Wawrinka has been replaced in the US Open draw by Germany's Florian Mayer.
