Rafael Nadal has been unhappy with the Madrid Open since it moved on the schedule from the hard-court season, and now he's blaming the ATP for the introduction of a blue-clay surface.

The six-time French Open champion was troubled when he practiced on the court for the first time Thursday. He described it as soft and slippery and criticized the placement of advertising boards at either end as too low and the same color as the surface.

A longtime critic of this event's organizers, Nadal is upset the ATP allowed the change in the middle of the clay season.

"My thoughts haven't changed on the concept and organization of this tournament," Nadal said Friday. "My criticism is not directed at the tournament but at the ATP, which should never have allowed such a change at a tournament of this scale."

In an email to The Associated Press, the ATP said tournament organizers completed all the necessary testing for its approval.

"The ATP granted this permission for one year with the understanding that it will be reviewed following the event, of course taking into account feedback from players," the ATP said in the statement. "We believe it is a good thing that our tournaments are trying to be innovative."

Nadal hasn't been a big fan of the tournament since its schedule move in 2009, unhappy that the high altitude and thin air of spring in Madrid negates the strengths of his game and helps his rivals.

The second-ranked Spaniard is 33-2 in career clay-court finals but 1-2 in Madrid.

"This is a clay-court event that is least like a clay-court event. There is always a chance of playing worse here," Nadal said. "I only speak my mind for the good of the tour and the players, so that we have a clay tournament with few problems."

Nadal lost last year's final to Novak Djokovic, who was in the midst of a 43-match winning run. He finally beat the top-ranked Serb in a championship match after seven straight losses, capturing his eighth Monte Carlo Masters title on April 22. He followed it with a win at the Barcelona Open a week later.

"It's practically unrepeatable and impossible for what he did last year to happen again," Nadal said of Djokovic. "It's been two positive weeks and things are on the right path. I'm happy with how I am playing."


AP Sports Writer Howard Fendrich in Washington contributed to this report.