I found this story, which has been covered in The Guardian and elsewhere, interesting from a legal standpoint. It seems, according to Time's take on it, that had this author written the book in Johanssen's home country of the United States, the First Amendment would probably have protected him.
Scarlett Johansson is suing French novelist Grégoire Delacourt €50,000 (£41,000) in damages, alleging that his work of fiction - La Premiere Chose qu'On Regarde"(The First Thing We Look At),- makes fraudulent and damaging claims about her personal life. The book tells the story of a French model who looks so similar to the American actor that the book's lead male character thinks it is actually Johansson. In the novel, the model's looks mean that men see her only as a sex object, while women are jealous of her. She has a series of adventures as Johansson until she is eventually found out and ultimately dies in a car crash.