Movie bosses are scratching their heads after George Clooney's much-hyped new movie Leatherheads flopped at the U.S. box office on its opening weekend.

The American football comedy, which Clooney directs and stars in, was expected to top the charts this weekend, after an aggressive marketing campaign.

But Leatherheads took just $13.5 million, finishing in second place behind gambling movie 21, which earned $15 million in its second week of release.

Now bosses at studio Universal are concerned the movie will fail to make a profit on its $58 million budget.

Universal spokesperson Nikki Rocco tells the New York Daily News, "I'm disappointed for George. I think he's a great guy and he's got tons of directing talent. I wish I could tell you what went wrong."