MADRID - The Madrid Open was in danger of losing two of its star attractions for next year's edition after Rafa Nadal and Novak Djokovic said they would boycott the Masters event unless organisers ditched the controversial blue clay courts.

World number one Djokovic and number two Nadal have been the most vocal in attacking the new surface, which organisers argue makes it easier for TV viewers to follow the balls but many players say is much more slippery than traditional red clay.

Nadal was dumped out in the third round on Thursday when he was upset by 15th seed Fernando Verdasco, the French Open champion's first defeat on clay in 23 matches and his first loss to his Spanish compatriot in 14 meetings on all surfaces.

"The ATP and the tournament can do what they want," a visibly irritated Nadal told a news conference.

"I tried my best to prepare but I wasn't good enough to adapt my game to this court," added the 25-year-old, who was chasing a third straight clay title of the season.

"The only thing that I know is that if things continue like this I am very sad but next year will be one less tournament in my calendar."

Organisers declined to comment, while the ATP said the blue courts are a one-year experiment and a decision will be taken on whether to keep them for 2013 once all feedback had been considered.

Djokovic slammed the Manolo Santana centre court after his laboured second-round victory on Tuesday and joked that he was considering wearing football boots or enlisting the help of action star Chuck Norris to help deal with the slick surface.

He slipped and slid his way to a 7-6 6-4 win against unseeded Swiss Stanislas Wawrinka on Thursday before announcing he would not play in the Spanish capital next year unless the red clay courts were reinstated.

"They are saying it's exactly the same as the red clay which is not true because there is a big difference," the Serb said.

"You are tripping and slipping and sliding all the time and winner will be the one who doesn't get hurt until the end of the week because a lot of players fell down," he added.

"Generally it's a new experience and the way it looks this year hopefully the last experience."

After his comfortable third-round win against Richard Gasquet on Thursday, world number three Roger Federer said he understood Nadal's frustration.

"He was against it from the start and so was I so obviously for him to go out in the third round is disappointing," the Swiss told a news conference.

"We never felt comfortable on the surface, it is a tough surface and that only makes you angry even more."

Nadal complained that having to play on a surface that is so different to the courts used at other tournaments, including the French Open starting later this month, was too disruptive.

"I think the tournament is great but that is a bad decision," he said.

"The movements are very important for me and here I cannot move so I cannot hit the ball the way that I want."

Although the blue clay is extracted from crushed brick, like the traditional red, the material is stripped of its iron oxide before being dyed.

The process has made the blue courts feel much slicker than the traditional red ones, which are typically slower.

"If you put the Cincinnati tournament on grass just before the U.S. Open do you think people are going to be happy? I don't think so," added Nadal.

"That's a similar situation. It's not drastic I am just being consistent.

"I am not prepared to risk something happening next year if nothing changes.

"I am going to Rome now with maybe a bit of a lack of confidence which I don't deserve after all the work I have put in here. The colour has to change and it has to be a proper clay court." (Reuters)