The mishap took place Sunday at the famous Mavericks surf spot, which is the site of one of the world's best known big wave competitions.
Butler, 42, was on location for the filming of the movie Of Men and Mavericks, the report said, when he was slammed by a wave more than five metres high and pinned underwater.
Butler was rescued by a safety patrolman on a jet ski and taken to hospital for observation, before being released.
Butler, star of films including the Spartan war epic 300, reportedly does not have extensive surfing experience, but has been working on his skills for the movie, in which he plays the mentor to a young daredevil surfer.
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