The man was standing on a bullbar while working on the engine of a four-wheel drive when he lost his footing and slipped.
He struck his head on top of the bullbar and sustained the serious injury.
He was transported by QAS to the Eurong helipad on Fraser Island to meet the Bundaberg RACQ CareFlight Rescue helicopter.
A QAS Flight Intensive Care Paramedic on board CareFlight’s helicopter treated the patient before he was flown to Hervey Bay Hospital in a stable condition.
The man was holidaying on the island at the time.