US Open champion Stan Wawrinka will not defend his title in New York later this month because of a knee injury.

The 32-year-old announced on Facebook he has had surgery on the problem and will return to action in 2018.

Last month, the Swiss struggled and needed ice on his knee as he was knocked out in the first round of Wimbledon by Russia’s Daniil Medvedev.

“I love this sport and I will work hard to get back to my top level and play many more years,” said Wawrinka.