Federer, 40, told Swiss media he's unlikely to return to competition until mid-2022 as he recovers from multiple knee surgeries and would be "extremely surprised" if he was able to play at Wimbledon, where he's won eight times.

The 20-time major champion said he would be able to resume running in January and return to training on court in March or April. He reckoned he was still hoping for a "miracle" when he returned.

"Roger is an icon of our sport and people around the world love him," said Djokovic, after securing a semi-final spot at the ATP Finals with a 6-3 6-2 victory over Russian Andrey Rublev.

"They love watching him play, love seeing him around.

"He's very important for our sport, on and off the court.

"For the sake of our sport, I sincerely hope that we can see him play at least another time. I'm sure he doesn't want to end his career this way.

"I think he's going to definitely give it a last push, a last try. For everything he has achieved and created for this sport, he deserves to play and deserves to have a proper farewell."

Djokovic is looking to match Federer's record of six titles at the season-ending ATP Finals.

"I need to be very patient and give my knee the time to heal. The next few months will be crucial," Federer said in an interview carried by several Swiss media outlets.

"This summer it was decided to suture the lesion to my meniscus, which involves some downtime.

"The doctors took the opportunity to also treat my cartilage. The combination of these two procedures requires patience and caution."

Federer has not won a grand slam since clinching the Australian Open title in 2018 but added: "My life is not going to collapse if I don't play a grand slam final again.

"But it would be the ultimate dream to go back. And in fact, I still believe in it. I believe in these kinds of miracles."

Australian Associated Press