By Andrew Downie
SAO PAULO (Reuters) - Former world number one Rafa Nadal has renewed his attack on hard courts as he prepares for the second tournament on his comeback trail at the Brazil Open.
The 26-year-old Spaniard, who returned to competitive action at the Chile Open last week after a left knee condition sidelined him for seven months, said the number of tournaments played on hard surfaces would limit players' careers.
He also criticized a move to speed up matches by strictly enforcing the 20-second rule between points at grand slams.
"Hard courts are aggressive on the knees, back and ankles," the 11-times grand slam champion, told reporters in Sao Paulo.
"That is a theme among the players and doctors. To make a change like that (reduce the amount of hard court events) it won't be possible in this generation but I think that the ATP has to work to think of how to lengthen tennis players' careers.
"Can you imagine football players playing on cement?"
Nadal has often been criticized for the length of time he takes between points but warnings for slow play have been few and far between.
ATP chiefs recently agreed that umpires would be expected to enforce the 20-seconds between points rule at grand slams, prompting criticism from leading players.
"Rule changes should be made to improve the sport," he said.
"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. Twenty five seconds is not enough."
Seven-times French Open champion Nadal was surprisingly beaten by Argentina's Horacio Zeballos in the final of the Chile Open, raising concerns about his recovery.
He said on Tuesday that his knee was still painful most of the time but was improving.
"I am a little tired after a tough week in Chile that came after weeks without competing," he said.
"But I am motivated to play and that gives me energy. Physically, it isn't that I am bad, it's just that the knee hurts some days."
"The positive thing it that if a month ago 80 percent of the time my knee hurt, now it is 70 percent of the time and next week or next month it will be 50 percent of the time.
"Each week the number of bad days is less."
Nadal, who won the tournament the last time he played in it in 2005, will play a doubles match with Argentina's David Nalbandian later on Tuesday before opening his singles campaign two days later.
He acknowledged the long lay-off had been worrying but said he no longer had any fears the injury might end his career.
"It is normal to have doubts," said the 11-times grand slam champion. "I am very confident that it will improve and the doctors say the same and that is what is important.
"I am not worried that it could be a problem in the future."
(Editing by Martyn Herman)