A 23-year-old man was hit over the head with a glass bottle during a night out in the centre of Brighton.
The attack happened at about 10.30pm on Saturday night (23 February) in the Castle Street area, close to Churchill Square.
Two men had been seen arguing shortly beforehand, Sussex Police said.
The suspect was described as black, about 5ft 10in tall, of large build and with short black hair.
The victim was taken to the Royal Sussex County Hospital in Brighton for treatment and later discharged.
Anyone with information can call Sussex Police on 101 or the independent charity Crimestoppers anonymously on 0800 555111.