Melbourne - Rafael Nadal has criticised Roger Federer for letting other players "burn themselves" by complaining about tour conditions while maintaining his good reputation by rarely making negative comments about tennis.
The pair have always been respectful rivals, but the ongoing debate about the overcrowded tennis calendar has exposed a difference of opinion on the eve of the Australian Open.
After telling a pre-tournament news conference on Sunday he had no intention of being the frontman for the players' grievances because it has reflected badly on him in the past, Nadal was then critical of 16-time Grand Slam winner Federer in a Spanish-language interview.
Responding to the suggestion that Federer disliked players complaining openly about problems on the tour because it tarnished the image of tennis, Nadal said he took another view.
"No, I totally disagree," he said in comments translated from Spanish. "For him it's good to say nothing. Everything positive. 'It's all well and good for me, I look like a gentleman,' and the rest can burn themselves.
"Everyone is entitled to have their own opinions."
Nadal and No 4-ranked Andy Murray are among the players who have been outspoken in recent months on issues including an overcrowded calendar and the scheduling of Davis Cup matches. Some players have talked of strike action as recently as Saturday's player meeting in Melbourne; Nadal has said players may have to resort to "strong action" if there isn't an "evolution" in the calendar.
Federer and Nadal, who has 10 Grand Slam titles, dominated men's tennis for the seven years before Novak Djokovic won three of the four majors in 2011 and overhauled them both for the No 1 ranking.
They're both key ambassadors for the tour, helping with promotional work and appearances at tournaments around the globe.
Nadal thinks that when the majority highlight problems on the tour, the intention is to make it better, not run it down.
"He likes the circuit. I like the circuit," Nadal said. "It's much better than many other sports but that doesn't mean that it couldn't be better. It doesn't mean there are some things about the tour that could change. The tour is fine, but there are some things that are bad. That's all we're saying.
"And the vast majority of players have this same opinion. He's got a different opinion ... if the vast majority have one opinion, and a small minority think differently, maybe it's them who are wrong."
For the first time since the 2005 French Open, Federer and Nadal are on the same side of the draw at a major, which means only one of them can reach the final on January 29.
They both start Monday. Third-seeded Federer, a four-time Australian Open winner, is on Rod Laver Arena in a night match against Russian qualifier Alexander Kudryavtsev.
No 2-ranked Nadal has the last match on Hisense Arena - the second show court at Melbourne Park - against Russian Alex Kuznetsov.
Defending champion Djokovic doesn't start until Tuesday. Women's champion Kim Clijsters is third match on Rod Laver Arena on Monday against Maria Joao Koehler of Portugal.
Li Na, who lost the Australian final last year but rebounded to win the French Open to become China's first Grand Slam singles champion, has a first-round match against Ksenia Pervak of Kazakhstan and No 1-seeded Caroline Wozniacki, still searching for a maiden major title despite finishing the last two seasons with the top ranking, faces Australia's Anastasia Rodionova.