Michael Hayes, 39, left Destino restaurant on Hope Island on Saturday night and was seen speaking to a man outside at 9.20pm.
Queensland Police detective inspector Chris Ahearn said the man delivered “one blow to the head” causing Hayes to “collapse to the ground”.
The man is described as Caucasian, between 20 and 30 years old with short dark hair.
Police believe he was wearing dark tracksuit pants, a dark long-sleeved shirt and an over-the-shoulder satchel.
The man is known to police however detectives believe he is not a part of an outlaw motorcycle gang.
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Hayes was taken to Gold Coast University Hospital where he remains in a critical condition with his family by his bedside.
“Our thoughts go out to them,” Ahearn said.
“He is on life support at the moment and we hope that he pulls through.”
Police are searching for CCTV as their investigation continues.