The 'Machine Gun Preacher' star got trapped underwater after he was hit by a series of waves while filming 'Of Men and Mavericks' – which tells the true life story of late surfing icon Jay Moriarty – at the infamous big-wave Northern Californian surfing spot Maverick's.
The 42-year-old actor – who plays champion surfer Ricky 'Frosty' Henson in the movie – got caught in a 12ft swell before he was pulled from the water onto a jet ski and then taken to shore and driven to Stanford Medical Center for overnight observation.
Eye witness and surfer Frank Quirarte wrote in his ESPN Action Sports Blog: “Butler was held down for a solid two-waves and took four or five more waves on the head.
“He was then washed through the rocks on the inside before he was finally able to be plucked out.
“Even on small days the inside at Maverick’s can push 10ft plus and really tear you up.
“When they brought Butler in he had that 100-yard stare that surfers get after a two-wave hold [down] or near death experience.
“After almost 20 years at Mavericks I’ve seen a lot of it, but at least he was standing on his own two legs. He was then carted away in a waiting ambulance.”
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Despite the huge waves, Frank insisted Gerard – who has been training at the location throughout the summer to get in shape – and the film crew were "chomping a the bit" to get in the water.
He added: "With Maverick’s and the entire Northern Hemisphere big-wave season off to a slow start surfers and the film crew were chomping at the bit to get a few days of surfing and filming in.
“Waves were running at 12ft, but some large ones had got through.
"Butler had no business to go near the bowl."
The incident comes almost eight months after Hawaiian surfer Sion Milosky died in a near identical incident at Maverick's.
Stanford Medical Center and Gerard's representatives would not comment on his condition on Monday.