A woman suffered facial injuries when she was attacked in the street in Brighton.
She was taken to the Royal Sussex County Hospital where, Sussex Police said, she underwent six hours of treatment.
The force has issued a picture of the suspect and asked for help from the public to identify him.
Sussex Police said: “Police in Brighton want to interview him about a late night city centre street attack on a woman which left her with facial injuries needing six hours of hospital treatment.
“The incident happened shortly after midnight on Thursday 4 October while the victim, a 21-year-old local woman, was with a friend outside the Regency Leisure Arcade, in West Street, Brighton.
“A group of two men and one woman walked past – and one of the men, described as white, aged between 18 and 21, about 6ft, with short brown hair, wearing a blue Nike hoody and with a backpack, punched her in the face before walking off.
“The victim sustained facial bruising and was treated at the Royal Sussex County Hospital.”
PC Andre Owen said: “This was an unprovoked attack by a complete stranger but we think people who see this CCTV image may be able to put a name to him.
“If you can help, please contact us.
“If you have any information about the incident or suspect, contact police by emailing 101@sussex.pnn.police.uk or call 101, quoting serial 731 of 05/10.”
