Model Kate Upton is threatening to take legal action against the owners of a celebrity spoof website after editors posted a fake topless photograph of the beauty online.

Bloggers at Celeb Jihad published a digitally altered picture of the Sports Illustrated star with her breasts exposed under the headline 'Kate Upton Naked Outtake From SI Swimsuit 2014.'

The image was quickly identified as a fake, but Upton's legal representatives are now demanding site bosses remove the explicit snap - or face them in court.

In a letter obtained by Tmz.com, the lawyers complain, "One of these photographs has even been airbrushed."