Fassbender has won a string of honours for his portrayal of a sex addict in the movie, and was also tipped for a Golden Globe and BAFTA.
He was widely expected to be nominated for a Best Actor Oscar, but was left off the shortlist when it was announced last month (Jan12) - and British-born McQueen is sure the edgy film cost its star a place in the category.
He tells the Press Association, "In America they're too scared of sex, that's why he wasn't nominated. If you look at the best actor list you're saying, 'Michael Fassbender is not on that list?'
"It's kind of crazy. But that's how it is, it's an American award, let them have it. He's a once in a generation actor. He's an actor who can transform and transcend, and you actually believe him, so that's the kind of guy he is."
Brad Pitt, Gary Oldman, Jean Dujardin, George Clooney and Demian Bichir will fight it out for the prize at the ceremony on Sunday (26Feb12).