Police were called to Greenstead Social Club, Blackthorn Avenue, Colchester shortly after 10.05pm on Friday 5 May.
Officers and ambulance service colleagues attended and found a man, 20s, unconscious, outside in a car park.
He had sustained a head injury and was taken to hospital, where he remains. At this stage, his injury is considered life-changing.
A man, 26, has been arrested on suspicion of GBH and remains in police custody.
Do you have any information?
If you have any information, CCTV, dash cam or other footage in relation to this incident, then please get in contact with us.
You can let them know by submitting a report online
Alternatively you can call us on 101.
Please quote crime reference 42/81182/23 when providing any information to make sure it gets to the right person as quickly as possible.
