Federer won the Australian Open in January
Roger Federer has pulled out of the US Open after revealing he will undergo another knee operation in September.
The 35-year-old Swiss star has undergone two operations in the last year – the second on his surgically repaired left knee.
Federer won his 20th Grand Slam title at Wimbledon this summer, beating Marin Cilic in the final.
But the world number one has ruled himself out of the US Open after announcing surgery will be carried out on his left knee.
“The surgery is not actually scheduled for this week,” Federer told reporters at the Cincinnati Open.
“I’m still waiting for that to happen, but I’m definitely going to play at the US Open. We’ll see the surgery, hopefully, in September.
“This is great for me to be able to have, three weeks from the start of the US Open, I won’t be ready.”
Federer had not ruled himself out of the US Open in New York, which starts on 23 August, and the delay in getting the operation means he will not be able to compete for the defence of his Australian Open title next month.
“It’s been so long – I’ve had a tear in my left knee for a while now and it was slowly getting worse,” he said.
“I’ll have the surgery and I’m hoping to be 100% by Christmas. I’d like to play well after Christmas.
“I’m going to have to look beyond the Grand Slams for now.”