The Harry Potter star, who was named as a "frontrunner" for the erotic adaptation last week, told Entertainment Weekly that she has not even read EL James's bestseller.
"I haven't read the book, I haven't read a script, nothing," she said. "There are so many movies you become attached to when I've literally never even received a phone call.
"It was the same way with The Girl With the Dragon Tattoo - I never even saw a script!"
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Watson added that many of her friends asked her about the Fifty Shades rumours after they emerged last week.
"I told them just because there are 60 articles on the internet doesn't mean it's any less true than if there are three or four," she commented.
Watson came fourth in a recent Digital Spy casting poll to find the ideal Ana. Game of Thrones actress Emilia Clarke was placed in first, while The Vampire Diaries star Ian Somerhalder was first in the voting to play BDSM-loving tycoon Christian Grey.
Stars such as Emma Roberts and Lucy Hale have been linked to the Ana role. True Blood actor Alexander Skarsgård has expressed a desire to play Grey.
The Social Network and Moneyball producers Mike De Luca and Dana Brunetti will oversee the film adaptation for Universal and Focus Features.