Roger Federer said he was "clearly an underdog" for the Australian Open and admitted to some uncharacteristic nerves on Saturday as he pondered a treacherous draw.

The 35-year-old, back from a six-month injury lay-off, is seeded 17th at Melbourne Park, complicating his attempt for a record-extending 18th Grand Slam title.

Two days from the start of the tournament, Federer was still in the dark about his first-round opponent as the qualifying rounds continued.

"Is it a lefty, a righty? It's a big deal. Is he a big server, a grinder?" said the Swiss.

"A bit of an unknown here the first round because that's the part of the draw I care most about because of having not been playing."

Federer's path is strewn with hazards, as he faces potential matches with Tomas Berdych and Kei Nishikori before a possible quarter-final with world number one Andy Murray.

It's a prospect to give even the ice-cool Swiss pause for thought as he tries to craft his comeback from the longest injury break of his career, prompted by knee problems.

Federer's absence raised inevitable questions about retirement, but he said he was delighted to be back in a Grand Slam draw — even in the unaccustomed role of underdog.

"Yeah, why not (underdog) for a change? I mean, I prefer to be the favorite. Underdog is okay. Yeah, it's fine," he said.

"As long as I'm healthy and I feel like I can go four, five sets, I can go many matches in a row, then I think it's going to be fun."

He added: "It's a great draw because I'm in the draw. So for me I'm super-pleased that I made it here, that I have an opportunity to win matches.

"How many remains to be seen. I'm cautious myself. So, yeah, clearly an underdog this time around."

Physical fitness could be a factor in what can be the most gruelling conditions of the year, with temperatures forecast to soar towards 40 Celsius (104 Fahrenheit) next week.

Federer has played only three singles matches since July, but he said he had been trying to simulate the endurance needed for five-set Grand Slam encounters in training.

"I trained as hard as I possibly could, so I will be ready for it. I did numerous sessions where I trained over two-and-a-half, three hours," he said.

"I feel I'm ready. But, like I said, it is the unknown.

It's the part that I can only know once I've been there."

Just walking on court will be a pleasure for the father of four, who said he had missed the atmosphere on tour during his time away from the court.

"I guess you do miss the matches at some point. You miss the feeling of winning, walking onto a stadium, seeing the guys," he said.

"You know, it's like an extended family to some extent anyway. You walk around here… you see faces you haven't seen in a while. It's just nice to see everybody again."