Roger Federer "is a little uncertain" when he will be back in action just over a fortnight before the US Open gets under way.
The 20-time grand slam winner withdrew from both the Canadian Open and Cincinnati Masters this month as he continues to recover from a knee injury.
Federer has not played since losing to Hubert Hurkacz.in a Wimbledon quarter-final in July and has completed only five events this year.
The legendary Swiss, who underwent two operations on his right knee last year, is unsure if he will feature at Flushing Meadows.
He told Swiss newspaper Blick: "I haven't done anything for a long time because of my knee. After Wimbledon, I had to let everything sink in first.
"This week I'll meet my doctors and my team and then we'll see what happens next. At the moment everything is still a little uncertain."
Federer, who celebrated his 40th birthday last Sunday, remains upbeat despite such uncertainty.
He said: "You have to adapt. It has always been like this in my career. Factors change: degree of awareness, successes, experiences, identity and now just that.
"I'm a quiet guy who takes things with a sense of humour. I always see the good in every situation. If it's not good right now, I know it will get better and it could be a lot worse.
"I am doing very well. My family is healthy. I just turned 40 and I'm still active. Who would have thought it? Certainly not me. I am totally at peace with myself and I am sure that there will be a lot more beautiful things to come."
Novak Djokovic drew level with Federer and Rafael Nadal on 20 major singles titles by winning Wimbledon and the world number one will be bidding to complete a calendar Grand Slam in New York.
