Rafael Nadal to test Novak Djokovic, star coaches at Australian Open

World number one Rafael Nadal will attempt to dethrone Novak Djokovic and put a new wave of celebrity coaches to the test when he returns to the Australian Open next week.

Nadal missed last year's edition during a seven-month injury break with knee trouble before making a stunning comeback to win 10 titles in 2013, including the French Open and US Open.

Now the rampant Spaniard will take aim at Djokovic's three-year reign at Melbourne Park, the longest of the Open era, and try to avenge his epic, six-hour loss to the Serb in the 2012 final.

He also arrives as the only "Big Four" player without a star coach, after Djokovic and Roger Federer, aping Andy Murray's move in hiring Ivan Lendl, hooked up with Boris Becker and Stefan Edberg respectively. (Also read: Rafael Nadal prefers continuity to celebrity coaches)

However, with Murray returning from injury and Federer now 32, the door could be open for a group of other contenders, led by Juan Martin del Potro and David Ferrer.

Nadal, still coached by his uncle, Toni Nadal, underwent a new but undisclosed form of treatment on his injury-prone knees in the off-season, and he appears confident he can stay healthy in 2014.

"I feel that this (treatment) really makes me feel more comfortable," he said in Doha, where he started his season by winning the Qatar Open.

"Because I don't have pain like I had, no?"

Nadal's 2012 Melbourne appearance ended in the small hours and defeat to Djokovic following a Slam-record five-hour, 53-minute final, after which the Spaniard told the crowd: "Good morning!"

In Nadal's absence last year, Djokovic showed similar powers of endurance when he ground down Murray in a physical four-setter to clinch his third straight Melbourne title. (Related: Nadal's atonement brings New Year resolution)

It turned out to be the high point of Djokovic's year and after losing the Wimbledon and US Open finals, he ceded the top ranking to Nadal at the China Open in September.

However, he sent out a message by beating Nadal soundly in the Beijing final, ending the year with a four-title run culminating in another big win over the Spaniard to take the World Tour Finals in London.

Despite this strong finish, Djokovic sprang a surprise by hiring Becker, the German great with little experience of coaching, in a move thought to be aimed at adding more adventure to his game.

He is not the only one, with 17-time Grand Slam champion Federer acquiring the services of childhood hero Edberg as he seeks to extend his stay at the top of men's tennis.

Federer, also sporting a new, bigger racquet this year, kicked off the new season by reaching the Brisbane final, only to be shocked by fellow 30-something Lleyton Hewitt.

And with Murray only just returning to action after back surgery, there could be an opportunity for the likes of del Potro, Ferrer, Tomas Berdych or Stanislas Wawrinka.

The timing of the year's first Grand Slam, just days into the new season, also makes it unpredictable, with players not always into their rhythm and match fitness.

"It's difficult because the Australian Open is very early. It would be better to play it a bit later," admitted Nadal.

"It can be only the second tournament (of the year) that you are competing in, and it's one of the most important, so it's a bit strange."

Japan's Kei Nishikori has followed the celebrity trend by hiring Michael Chang, while Richard Gasquet has enlisted two-time French Open winner Sergi Bruguera.

Talented but wayward Australian number two Bernard Tomic will be followed closely by home fans, and Wawrinka has shown he's a man in form by winning last week's Chennai Open.