04:04 AM ET  01.12 | But the Serb said Nadal's extended absence with knee problems proved that tennis remained unpredictable - and that there were a host of players waiting to take advantage if the top men falter. "I think we cannot predict anything. It's individual sport, so it only depends from you. Anybody can have what Nadal has at this moment," Djokovic said in Melbourne. "That's why you have to be so committed and professional for daily routines. Small details matter for long term, the preparations you do, the practice, the recovery. "If you are injured, you're off the tour. Your ranking is going down." Argentina's Juan Martin Del Potro is the only man besides Djokovic, Nadal, Roger Federer and Andy Murray to win a Grand Slam tournament since 2005. Nadal, an 11-time Grand Slam winner, missed much of last season with ongoing knee problems, and announced his withdrawal from the Australian Open last month citing a stomach bug. "It's probably expected that the three of us, and Nadal of course, would still be main candidates to win all the major titles," Djokovic said. "But, you know, I wouldn't underestimate Del Potro, (Jo-Wilfried) Tsonga, (David) Ferrer, (Tomas) Berdych, anybody who is in the top 10. I'm sure there's new young players coming up like (Bernard) Tomic, (Grigor) Dimitrov, (Milos) Raonic. driverlap.blogspot.com