Matthew Fox and Ed Harris have backed out of World War Z.

The Lost veteran joined the cast of the zombie film in mid-June to play the role of 'Parajumper'. However, the deal has since fallen through due to a scheduling conflict with Fox's other project I, Alex Cross, according to New York Magazine.

Meanwhile, Ed Harris has been in talks for the film since mid-June, but the negotiations have reportedly fallen through for unspecified reasons.

With the movie slated for a 2012 release, filmmakers are apparently rushing to recast the roles left vacated by Fox and Harris.

World War Z will feature Brad Pitt, The Killing's Mireille Enos, Adjustment Bureau star Anthony Mackie and The Pacific's James Badge Dale.

Based on Max Brooks's novel of the same name, World War Z is set ten years after humanity triumphed over a zombie apocalypse and tells the story of those that survived the conflict.