World number 4, Stan Wawrinka has quit tennis for the rest of 2017 due to surgery on his injured knee and will not defend his US Open title.

The 32-year-old Swiss struggled with the knee injury when he was knocked out in the first-round of Wimbledon by Daniil Medvedev last month.

In a statement on his official Facebook page, Wawrinka said: “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.”

“This was the only solution to make sure I will be able to compete at the top level for many more years.”

BREAKING: Our 2016 #USOpen champion, @stanwawrinka has withdrawn from the 2017 tournament due to a knee injury. https://t.co/VthrbNhgSX pic.twitter.com/pVhD0b1GJW

— US Open Tennis (@usopen) August 4, 2017

Stan Wawrinka won the US Open last year, beating Serbia’s Novak Djokovic at Flushing Meadows to earn his third grand slam title.

Wawrinka joins Novak Djokovic in quitting the rest of the 2017 tennis season, and it’s still uncertain if world No1 Andy Murray will recover in time from his hip injury to compete at the US Open.