A 24-year-old man suffered a serious head injury when he was attacked in West Street, Brighton.
He was punched and knocked to the ground outside the Oceana nightclub by another man near the taxi queue at 3.20am on Sunday 25 November.
A 29-year-old Hove man was arrested at the scene on suspicion of assault causing grievous bodily harm, questioned and released on bail until Friday 11 January.
The victim was initially treated for a head injury but his condition has since deteriorated and he is being treated in Hurstwood Park Neurosciences Centre in Haywards Heath.
Detective Melanie Wauchope said: “The victim has suffered a serious head injury and is still in hospital.
“We are keen to hear from any witnesses.”
Anyone with information is urged to call Sussex Police on 101.
