The American, nicknamed Foxy Knoxy, remains at large in the US while appealing to Italy's Supreme Court. If she loses her final appeal she will become a fugitive, and the subject of a high profile extradition tussle.
Knox's lawyer Luciano Ghirga pointed out that Knox's case was still ongoing, and said the American creative writing graduate would sue if the film "was damaging to her image."
He said he hadn't seen it but "supposed - knowing the author - that it implies that Amanda is guilty".
"There have already been at least two films and 12 books about the case. If the film is based even loosely on the murder in Perugia and if it is damaging to Amanda's image, we will be asking for damages, as we have done in other cases."
But the writer insists the film does not "place the knife in Knox's hand".
But the Kercher family, who were given a sneak preview of The Face of an Angel, have given their apparent blessing to the film, even allowing it to be dedicated to Meredith's memory.
Director Michael Winterbottom, who showed the film privately to Meredith's brother Lyle, said it was important to him to keep the victim at the centre of the story, rather than Knox .
Mr Winterbottom said: "The Kercher family had talked a lot about that, with a huge amount of dignity, the reasons they went for the trial was to make sure that amongst the chaos, it was remembered that someone had lost their life. That was one of the central things I thought about."
He said he had dedicated the film to Meredith only with the Kerchers' permission, telling Screen International: "I didn't want to do that unless someone from her family had seen it."
Miss Nadeau, played by Beckinsale in the film, explained: "There was a meeting in London with Michael and Lyle Kercher where he showed him the film. It was a very private thing. But if the Kerchers had objected to the film, the dedication to Meredith wouldn't have been there."
She said: "I remember worrying that a movie about this murder would be ultimately sensational, bloody, and disrespectful to Meredith Kercher, who didn't deserve to be a victim once more."
She told the Mail: "Anything with Knox as the star would be disrespectful to Meredith. But the film is not really about the murder, it just uses it as a jumping off point."
The writer claimed she was not worried about being sued, as she said the film does not "place the knife in Knox's hand".
Knox herself is played by Cambridge graduate Genevieve Gaunt, 23, who appeared as Pansy Parkinson, in Harry Potter and the Prisoner of Azkaban in 2004.
Formerly the love interest of Harry's arch-nemesis Draco Malfoy, the actress has now blossomed into a striking brunette, who bears an uncanny resemblance to Knox.
Watch the teaser trailer for The Face of an Angel below:
- Daily Mail