Director John Carney's film centres on a singer-songwriter (Knightley) who forms a bond with a down-on-his-luck record producer (Mark Ruffalo) after she is dumped by her rising star boyfriend (Levine).
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Green has been cast as hip-hop star Troublegum, who lends a hand to help the young singer fulfil her musical ambitions.
Hailee Steinfeld and Catherine Keener have also landed roles in the movie.
Filmmaker Carney previously scored an international hit with 2006's Once, which earned an Oscar for its song 'Falling Slowly'.
Can a Song Save Your Life? is expected to be released in 2013.
Watch Keira Knightley in the trailer for upcoming film Anna Karenina below:
