The prospects of an unprecedented 20th Grand Slam victory have strengthened for ageless wonder Roger Federer as his main rivals flounder ahead of the Australian Open.

The 36-year-old is coming off an extraordinary 2017, when he won a fifth Australian Open title and a record eighth at Wimbledon, and there could be yet more glory with a depleted field of top contenders in Melbourne.

Andy Murray and Japan's Kei Nishikori are already out of the year's opening Grand Slam with injuries, while 12-time major champion Novak Djokovic is troubled by an elbow complaint and hasn't played for six months.

World number one Rafael Nadal withdrew from his first tour event of 2018, in Brisbane, with continuing knee problems, and is seeking match practice in a Melbourne exhibition event ahead of the January 15 start.

The 2014 winner Stan Wawrinka, who hasn't played since last year's Wimbledon and subsequent knee surgery, has had little warm-up work and is no longer with his four-year coach Magnus Norman.

Yet amid it all Federer keeps going, winning all his matches at the mixed-teams Hopman Cup in Perth this month and seemingly injury-free.

"I just have to pace myself all the way up to the tournament in Melbourne, and I'll be ready," he said after his Hopman Cup final victory with Switzerland team-mate Belinda Bencic.

"I'm just excited going back to Melbourne where I had my fairytale run last year. It was crazy.

"It's great to be the defending champion. I take it the right way. I won't put extra pressure on myself, regardless of who's going to play, or not play.

"For me it's just important to be in a good mindset, well prepared, and ready to go. And I feel like I am ready."

- Kyrgios in good Nick -

Nadal, who lost to Federer in five sets in a vintage Australian final last year, has opted to join Djokovic at the Kooyong Classic exhibition event for some match practice in the week before the Open.

The Spaniard, who hasn't played since the World Tour Finals in London, had a stellar 2017, winning his 10th French Open, a third US Open crown and the year-ending world number one spot.

Six-time Australian Open champion Djokovic pulled out of events in Abu Dhabi and Doha with elbow soreness before heading to Melbourne, and hasn't hit a ball in anger since the problem forced him to quit Wimbledon in the quarter-finals in July.

Big-serving Canadian Milos Raonic is another with a chequered preparation after wrist surgery last year, while American world number eight Jack Sock hurt his hip while playing in the Hopman Cup.

The Australian Open is the second straight Grand Slam to be badly hit by injury issues.

The US Open was missing Wawrinka, Djokovic, Nishikori, Raonic and Murray, and after the early eliminations of Alexander Zverev, Marin Cilic, Grigor Dimitrov and Jo-Wilfried Tsonga, it was one of the rare Grand Slams where big names didn't dominate the quarter-finals.

If there is to be a winner outside the top guns in Melbourne, those who look most likely are Bulgarian Dimitrov, third in the rankings behind Nadal and Federer, Germany's Zverev and tempestuous Australian Nick Kyrgios.

Dimitrov, once nicknamed 'Baby Fed' for his playing style, enjoyed the best season of his career in 2017, winning four titles, including his first Masters crown in Cincinnati.

Zverev, 20, has been touted as the "next big thing" for some years and is coming off five titles last season, yet he has never made it past the fourth round of a Grand Slam.

Kyrgios will have his supporters, especially in Australia, after beating Dimitrov on the way to winning his fourth ATP Tour title and first at home in the lead-up Brisbane International.

"Right now it's all about recovering and feeling the ball for the Oz Open. Because obviously I'm playing well under pressure and in pressure situations," said Kyrgios, whose talent has often been undermined by petulant outbursts.

Other form players include France's Gael Monfils, who won the lead-up Qatar Open in a depleted field, and his countryman Gilles Simon who rolled back the years to claim the ATP Maharashtra Open title.