Event promoter Mike Porra told the Hamilton Spectator it was "the biggest trick attempted in the history of freestyle motocross."
Hours later, a video of the 26-year-old's double front flip attempt was posted online.
All did not go as planned.
Spectators at the event gasped in horror as they watched Cook violently crash into the ramp, suffering a serious spinal injury.
"Something snapped!" one man is heard shouting in the video.
[ Related: B.C. stunt biker seriously injured in Hamilton show ]
Watch Cook's terrifying crash below.
Paramedics removed Cook from the scene on a stretcher and rushed him to Hamilton General Hospital.
The next day, Cook posted a photo from his hospital bed after undergoing three hours of back surgery.
"This morning I underwent 3 hours of surgery on my back and I'll likely be in hospital in Ontario for the remainder of the week at which time I will transfer to BC. Again, thank you so much for all the support and positive messages. My mom and dad are here with me and helping keep spirits high. I've got this!" he wrote.
Lindsey Scott, a friend of the injured rider, told CTV News that Cook is concerned about the extent of his injuries.
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"He's got a really good support system and everybody’s rooting for him and sending him well wishes," she said. "His injuries have left his future kind of up in the air."
A double front flip has never before been successfully executed. Cook recently admitted to ESPN that before he started training for the record-breaking flip, he hadn't even attempted a single front flip.
"I don't even like doing front flips on trampolines," Cook said. "A month ago was my first time front flipping anything with wheels. I did a few fronts on a mountain bike, then put on my big boy pants ... and a diaper."
Porra told the Hamilton Spectator that Cook's injury is the worst the Nitro Circus Live Tour has ever had, and stressed that all competitors are highly trained professionals. Each trick is perfected in a foam pit before it's included in the show.
"You don't get on this tour unless you're the best in the world at what you do ... these guys are all full-time professional athletes before they came on the tour," he said.
The Hamilton event was the first-ever Canadian stop on the tour.
What lies ahead for Cook may be unclear, but the rider is determined to keep smiling:
"Go ahead, show off those chiclets and spread some contagious smiles. Dare you!" he wrote on Facebook, captioning a photo of himself giving the thumbs-up from his hospital bed.
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