The Swiss 17-time Grand Slam champion has not played a match since July when he tumbled during the final set of a loss to Milos Raonic in the semi-finals at Wimbledon
Roger Federer makes his long-awaited return to tennis after six months out with a knee injury in Sunday's mixed teams Hopman Cup in Perth ahead of next month's Australian Open.
The Swiss 17-time Grand Slam champion has not played a match since July when he tumbled during the final set of a loss to Milos Raonic in the semi-finals at Wimbledon.
Federer, 35, had surgery for the first time in his career on his left knee in February and after the Wimbledon set-back he did not finish the season, missing out on the US Open and Rio Olympics.
During his time out of the game Andy Murray and Novak Djokovic fought out the world No.1 ranking and his Swiss compatriot Stan Wawrinka won the US Open.
Federer makes his return with his world ranking down to 16, his lowest since 2001.
The Swiss legend, who will partner with Belinda Bencic, said he was looking to ease his way back before the start of the Australian Open in Melbourne on January 16.
"I'm really positive about how I'm feeling right now, and practice is going well," said Federer, who was watched by 5,000 fans at a practice session in Perth on Thursday.
"Expectations are low because I don't have the matches yet and it's going to be best-of-five from the get-go at the Australian Open.
"I'm happy I've got the Hopman Cup and I've got my three matches there to ease my way in."
Nick Kyrgios also makes his return in the Hopman Cup, but from a playing ban, after his spectacular meltdown at the Shanghai Masters in October resulted in an initial eight-week suspension.
A condition of the ATP reducing the ban to three weeks meant the controversial 21-year-old had to consult a sports psychologist to prepare him for the new season.
Kyrgios, who will partner with Daria Gavrilova in the Australian team, said he was now focusing on better managing his schedule and time.
"The added media interest is never easy and it's something that I haven't fully got my head around or got used to, but what can I do?" Kyrgios said.
"As far as how I'll deal with it, I'll just keep my head down and go about my business as I have done the past few Aussie summers."
Dual Wimbledon champion Petra Kvitova had pulled out of the Hopman Cup before she was knifed by a home intruder this month and required surgery on her racquet hand.
Kvitova will be out for six months and has been replaced in Perth by three-time doubles Grand Slam champion Lucie Hradecka, who partners with Adam Pavlasek in the Czech team.
Alexander Zverev, who teams up with Andrea Petkovic for Germany, says he is looking forward to his matches against Federer and Frenchman Richard Gasquet in his pool.
"It's been a great event to start the year off. It gives you a big advantage playing a few matches here," said Zverev, whose ranking has soared from 83 at the start of the year to a current 24.
Jack Sock and Coco Vandeweghe will be bidding to give the United States a record seventh victory in the Hopman Cup.
Teams (with current rankings):
Australia - Nick Kyrgios (13)/Daria Gavrilova (25)
Czech Republic - Adam Pavlasek (75)/Lucie Hradecka (165)
France - Richard Gasquet (18)/Kristina Mladenovic (42)
Germany - Alexander Zverev (24)/Andrea Petkovic (55)
Great Britain - Daniel Evans (66)/Heather Watson (76)
Spain - Feliciano Lopez (28)/Lara Arruabarrena (66)
Switzerland - Roger Federer (16)/Belinda Bencic (43)
USA - Jack Sock (23)/Coco Vandeweghe (36)