Jacques Villeneuve has hit out at drivers critical of Fernando Alonso's decision to tackle the Indy 500 next month.

Alonso will be racing next month in the legendary event in a McLaren-entered Andretti Autosports Dallara.

But some of his fellow F1 colleagues have questioned the wisdom of the Spanish driver taking on the dangerous and fabled American oval race with little preparation.

"I've already said that I think what he's doing shows that he's a real driver," Villeneuve, the 1997 world champion and a past Indy 500 winner, told the Spanish daily AS.

Asked what he meant by 'real driver', the French Canadian explained: "Well, all you have to do is listen to what other drivers have said about his decision.

"I heard Nico Hulkenberg and Romain Grosjean giving their opinion about what Alonso is doing -- Hulkenberg said it's dangerous, that he wouldn't do it, that he did Le Mans because it was different.

"It sounds like excuses," Villeneuve added.

"I think there are two classes of drivers. You're either an Alonso or you're a Rosberg. And Hulkenberg is a Rosberg."

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