Paris - Reigning US Open champion Stan Wawrinka will miss his title defence to have knee surgery, the world number four announced on Friday.
The three-time Grand Slam champion had already pulled out of the upcoming ATP tournaments in Canada and Cincinnati, and joins last year's US Open runner-up Novak Djokovic on the sidelines for the rest of the season.
"This was the only solution to make sure I will be able to compete at the top level for many more years," the Swiss said in a statement on Facebook.
"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.
"I will see you all in 2018!"
The 32-year-old Wawrinka, like Djokovic, will be hoping the time off can help him come back revitalised after a difficult month that included a first-round exit at Wimbledon.
On Thursday, Wawrinka admitted that the knee injury had hampered him during that shock defeat to unseeded Russian Daniil Medvedev in London.
The four-set victory over Djokovic in the final at Flushing Meadows last year gave Wawrinka his third major crown, taking him level with current world number one Andy Murray.
This season he has had fluctuating fortunes, but did reach his second French Open final where he was thrashed by Rafael Nadal.
Wawrinka will be hoping to emulate the Spaniard and his legendary fellow Swiss Roger Federer, after both returned from lengthy absences to claim Grand Slam titles this season.
Federer, 35, also did not play last year after Wimbledon, but has won both the Australian Open and Wimbledon this year and will be looking for a 20th major title in New York when the US Open gets underway on August 28.