Federer made a stunning return to the ATP Tour 12 months ago after injury, the Swiss winning his fifth title at Melbourne Park with a five-set victory over Nadal.

That success was the start of a sensational year that also saw Federer claim an eighth Wimbledon crown, while Nadal – who himself had recovered from injury – lifted the French and US Opens.

Heading into the opening grand slam of 2018, the pair have seen Andy Murray withdraw with a hip problem, while Novak Djokovic and Stan Wawrinka are expected to play after lengthy periods on the sidelines.

With a lack of fit challengers to Federer's crown, Philippoussis believes the evergreen 36-year-old can go all the way when the tournament starts on 15 January.

"To be quite honest with you, I think it's again either Federer or Nadal," the Wimbledon and US Open finalist told Omnisport when asked who the favourites were. 

"Federer's very special, what he did was incredible having six months off, coming back and winning his first event which happened to be a grand slam, the Australian Open.

"I'm not saying it's impossible [to happen again], but I don't expect that at all.

"I feel like those guys [Djokovic and Wawrinka], with the games they have, they have to feel their way in a little bit more, get some confidence under their belts before they can play their best tennis.

"It's great to have these guys back, but I just feel like they're going to need some matches and some tournaments to get back into it."

While the Australian Open may come too soon for Djokovic to challenge, Philippoussis anticipates the Serbian will be back on top of men's tennis again soon.

"Of course he can definitely come back to be number one in the world and win majors. But with him, it's just been mental over the past year," he said.

"And this is a guy that was so immensely strong and so mentally tough that nobody wanted to play him in a best of five sets. There was one stage where you couldn't beat him in a best of five sets, no one could, with his game physically and mentally.

"And he just lost that, maybe this time out, it's going to help him find his way back and get that mojo back, and like Federer maybe [he] needed some time off.

"That was obviously the best thing for him and hopefully this could be as well."