Roger Federer missed the Rio Olympics—and will skip the U.S. Open—to rehab his left knee, and will not play again in 2016. But he’s already gearing up for next season.

Federer underwent keep surgery to repair a torn meniscus following a semifinal appearance at the Australian Open, and then experienced a back problem during the clay-court season that forced him to withdraw from the French Open. He has not played since the semifinals of Wimbledon.

"I'll learn a lot from this year," Federer, speaking to reporters at a promotional event in New York City, said of the most injury-plagued season of his career.

Though he admitted that he does not know exactly what the problem is with the knee, Federer is back training, and said he is aiming to return for the Australian tournaments at the beginning of next season.

"I’m very hopeful, and positively confident, to be quite honest, that I will be fine," he said. "I think that, so far, rehab has been going well, and I’m looking forward to the next few months when I can start doing much more in the fitness room and also on the tennis court."

From the sidelines, he assessed the top contenders in Flushing Meadows, putting world No. 1 Novak Djokovic in front of the in-form Andy Murray despite the Serb's recent defeats.

"Novak is the favorite," said Federer. "He did win in Toronto. He has a great record against Andy and is a very good hard-court player. You see that in conditions like here and the Australian Open."

The 17-time Grand Slam champion also suggested that the new roof over Arthur Ashe stadium would help Djokovic, as it will feel like the Australian Open.

He did add, however, that he is "very impressed" with Murray, who has won or reached the final of his previous seven events and could potentially be in a position to compete for Djokovic's No. 1 ranking.

"I think it's going to be a great U.S. Open, and probably a very exciting race between them," Federer said.

Federer is No. 4 in the rankings.