At 3:44am on Sunday, August 16, police received a call from the ambulance service about a man who had been assaultedin the Holmeside area of the city centre.
Officers attended and the man, 38, was taken to hospital with serious injuries.
Enquiries were carried out into the incident and police believe the man may have been assaulted in a back lane opposite the Illusions bar.
Four men, aged 37,37,41 and 50, have been arrested on suspicion of assault and are currently in police custody helping with enquiries.
The injured man is in the RVI hospital in a critical but stable condition.
Anyone who was in the area at the timeof the assault and who witnessed it is asked to contact police on 101 ext 69191 quoting reference number 289 16/08/15.