Hartnett is starring in the West End until December
Hollywood actor Josh Hartnett is taking the Daily Mirror newspaper to court for alleging he had a "sexual dalliance" in a public area of a London hotel.
The 30-year-old, who is about to star in a West End production of Rain Man, said through his lawyers that he is seeking damages for defamation.
Hartnett is also seeking a public apology, according to the statement.
The Mirror story claimed that the actor was filmed on CCTV footage with a woman in the library of a Soho hotel.
It went on to allege that workers witnessed the incident.
The allegations are "not only untrue but a complete fabrication", said his legal representatives, adding they were "defamatory and unsubstantiated".
They also said that the story had been republished around the world.
Hartnett, whose screen credits include Pearl Harbor, is due to play Charlie Babbitt in the Apollo Theatre's production of Rain Man.
The role was portrayed by Tom Cruise in the Oscar-winning film.
The opening of the play, which is currently in previews, was recently put back a week to 19 September to allow new director Terry Johnson time to settle in.
A week's worth of rehearsal time was lost after the departure of original director David Grindley.