Keira Knightley has replaced fellow Hollywood leading lady Scarlett Johansson in Once director John Carney's new movie about a struggling singer.

Johansson was slated to show off her singing skills on the big screen in the film, A Song Can Save Your Life, opposite The Avengers co-star Mark Ruffalo, but she has pulled out of the project.

Reports suggest Ruffalo may have departed the film too - but True Grit star Hailee Steinfeld is still onboard.

In the film Knightley's singer character arrives in New York looking for love and meets a washed-up record producer.