MADRID - World No 1 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.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.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.