Rafa Nadal branded comments made by former French tennis player Yannick Noah about doping as "stupid" on Sunday, saying they were the words of a "kid".
In an interview in French newspaper Le Monde, Noah said the best way to combat doping was to legalise the use of drugs and also appeared to accuse Spanish sport in particular of using "magic potions".
Asked about Noah's comments at the ATP World Tour Finals where an ailing Nadal beat American Mardy Fish despite an upset stomach, the Spaniard was clearly angry.
"What's can I say? That's going to be difficult to explain what I feel in English," the 25-year-old 10-times grand slam champion told reporters.
"What he said is completely stupid and he knows better than nobody. To say that today is a totally stupid thing because you know how many anti-doping controls we are having during all the season year by year.
"So, in my opinion, his article, what he wrote, was from a kid. And when one kid say something, is not painful for us. So that's what I feel.
"I don't know how to say in English, but especially I think that's worse for France. Is worse for his country than for our country, in my opinion, because the image of the country when one guy, important guy like him, says that, is terrible."
Noah, the 1983 French Open champion, caused controversy when he spoke out in Le Monde on Saturday, saying: "Let's stop the hypocrisy. The best attitude to adopt is to accept doping. Then everyone will have the magic potion."
His comments drew scorn from France's sports minister.
David Douillet, an Olympic judo champion, responded by telling France 2 TV that the comments were "serious and irresponsible".
Spain's Olympic Committee president Alejandro Blanco said: "It is difficult for ignorant people to understand the boom of Spanish sport. It is hard work that has been the key to success."