Glenn Dickson, 25, underwent surgery in Cairns Hospital over the weekend, where he had his leg amputated after he was mauled off Hinchinbrook Island on Saturday.

The Muay Thai fighter's quick-thinking friends were credited with saving his life after dragging him from the water and applying a tourniquet to his savaged leg.

Channel Seven footage showed him yelling "I will survive" as he was wheeled into the hospital on Saturday evening.

"Brilliant Glenn.. survivor..fighter..inspirational human," one friend who noticed the declaration posted to his Facebook page.

The keen fisherman remained in a critical but stable condition on Monday morning.

An online fundraiser set up to help Mr Dickson, his pregnant partner Jessie Lee and their two kids had raised almost $20,000 by 8am.

Mates were rallying around the young couple online, urging their friends to donate and planning further fundraising efforts.

"Stay strong Glenn you're a f---ing inspiration!" one said.

"Seeing this stuff on the news breaks my heart but knowing the person involved is way too close to home," another friend said.

"This guy is a top bloke and such a loving and caring father, and partner to his fiancé."

Mr Dickson was attacked by what was believed to be a tiger or bull shark, according to reports from the scene, shortly after jumping in the water on Saturday.

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