Roger Federer said Friday the timing of his return to the courts was still uncertain, just weeks ahead of the US Open, but the tennis legend remained upbeat after turning 40. Federer, who has only played 13 matches in 2021, having been out for more than a year with two knee surgeries, pulled out of the Tokyo Olympics and subsequent tournaments to rest his knee. After turning 40 on Sunday, Federer said he was learning to adjust to the fact that recovering from niggles takes two weeks rather than two days. The US Open gets under way on August 30 but Federer did not say whether he would be taking part in the last of the year’s four majors. “I’m fine. I was on holiday. I haven’t done anything for a while because of my knee. I had to stop everything after Wimbledon,” he told Blick newspaper. “This week, I have to meet my doctors and my team, and then we will see what happens next. For now, everything is still a bit uncertain.” Federer reached the Wimbledon quarter-finals but pulled out of the Tokyo Games and then withdrew from the ATP Toronto and Cincinnati Masters — the last major tune-ups for the US Open. Federer said it was hard to deal with the uncertainty. “It was different before. The questions were simple: what is my place in the ranking? What will my next tournament be?”, he said. “Today, it’s more difficult: how do I feel when I start training again? What are my goals? How to reconcile all this with the family? What does the rest of the team say? “I am much more enthusiastic than before, the attitude is different. It’s really completely different from 10 years ago.” Federer is a 20-time Grand Slam champion, a record he shares with his younger rivals Novak Djokovic and Rafael Nadal. The sports star said he celebrated his landmark birthday privately with family and friends, and felt surprisingly good the following day. “I woke up in the morning when I was 40 and realised that everything was still the same as the day before. I was relieved,” he said.