Rafael Nadal, back in action after a seven-month knee injury absence, is blaming the ATP management for poor playing conditions at clay court events such as the ongoing Brazil Open.
After his straight-sets victory over Brazilian qualifier Joao Souza 6-3, 6-4 in his opening match on Thursday, the 11-time Grand Slam title winner had some harsh words over the choice of balls.
While other players have been complaining about the condition of the court at Sao Paulo's Ibirapuera gymnasium, Nadal said the problem lies elsewhere.
"The problem is not the court. The problem is the ball which is very bad," he told a post-match press conference.
"It's the fault of the ATP for allowing play with a ball of poor quality. The ATP does not have the capacity or the infrastructure to be able to analyze the conditions before the tournament begins."
The 26-year-old Nadal, who only returned to competitive tennis last week in Chile, also defended his decision to withdraw from a scheduled doubles match with Argentina's David Nalbandian against Horacio Zeballos and Oliver Marach Wednesday.
That, he said, was a "good decision" that allowed him to rest his knee, after a tough week of play in Chile last week where he made the final, losing to Zeballos.
Nadal was to play his Sao Paulo quarter-final later Friday against Argentina's Carlos Berlocq.
The Spaniard has been in combative mood all week.
On Tuesday, he told reporters that he and other players were concerned about the impact of having to play so many hardcourt events.
"Hard courts are aggressive on the knees, back and ankles," he said. "Can you imagine football players playing on cement?."
"That is a theme among the players and doctors," he added.
Nadal said that while reducing the number of events on hard surfaces was not realistic, "I think that the ATP has to work to think of how to lengthen players' careers."
And he also criticised the decision to enforce a 20-second rule between points at Grand Slams.
"Rule changes should be made to improve the sport," said Nadal, who has been no stranger to time violations in his career.
"I don't think the players in the dressing room are happy with the new rule and we'd like it to be modified and that the referee interpret when you can take longer rather than it be something mathematical.
"People want to see long rallies and hard-fought points," the world number five said. "Twenty five seconds is not enough."
Nadal, the top seed at the $US455,775 ($A442,457.04) Brazil Open, lost the singles and doubles finals at the Vina del Mar tournament in Chile on Sunday and plans to compete at the Mexico Open in Acapulco later this month.
The seven-time French Open champion won the Brazil Open in 2005 when it was held in Costa do Sauipe in eastern Bahia state.