World No.5 Juan Martin del Potro believes the top-four men's players are in a class of their own but he insists he will be ready to step up to their level at the Australian Open.
The Argentinian is back in the top five for the first time in more than three years and his game is again of a calibre that won him the US Open in 2009.
While Rafael Nadal, Novak Djokovic, Roger Federer and Andy Murray have dominated men's tennis for several years, the No.1 seed at the Sydney International believes he can match it with the big four.
''They are so good during every tournament and they are regular in the important tournaments,'' he said. ''They reach semi-finals and finals in every grand slam.
''I was close to reaching the final in Wimbledon but it wasn't enough to win there. I have to be ready for the moment, like I was in 2009 when I beat Rafa [Nadal] and Federer in semis and finals.
''I was ready for the moment and I think I've been training hard trying to find that moment.
''I think I'm ready to keep fighting with them in the grand slam but they are still so good and the biggest favourites.''
Del Potro, who has a career-high ranking of No.4, has taken a few seasons to return to the top after plummeting to No.485 because of injuries.
''I'm in the top five after three years and a half, and I see a good opportunity to keep improving my ranking, but I also feel a little difference between the top guys and the rest and me. I'm looking forward to playing most tournaments healthy. That could be my biggest goal for this year,'' he said.
The 25-year-old, who played the Kooyong Classic before last year's Australian Open, said the Sydney International was a good litmus test for this year.
''I think it's a good chance to see how I'm feeling before the grand slam. It's a good opportunity because it's a 28-player draw,'' Del Potro said.
''If you play good matches you go far really quick, but I'm also thinking about the grand slam and it's very important to start the year much better than I did in 2013.''
He said he expected defending champion Bernard Tomic to cause a few problems for higher-ranked players.
''[He] is still young. He has a big future. He's already made good tournaments and beaten big players, but he's young. He's going to be a really dangerous player for us this season and in the future, too.''
On day one of the men's draw, Russian Alex Bogomolov jnr beat Australian John-Patrick Smith (6-4, 6-3); American Ryan Harrison beat Frenchman Stephane Robert (6-3, 6-2), and Czech Jiri Vesely beat Australian wildcard Jordan Thompson (6-7, 6-3, 6-1).