An unprovoked attack left a 50-year-old man with a fractured eye socket.
The victim was walking in St James's Street, Brighton, at about 2am last Friday, August 8, when he was approached by a man who asked him for a cigarette.
Without warning, the attacker then punched the victim and ran off along St James's Street.
The attacker was white, about 30 years old and 5ft 6in with scruffy brown hair.
The victim did not report the incident to police until two days later.
Detective Constable Melanie Wauchope said: "This was a nasty attack in an area of the city that could have had quite a few people in it at that time on Friday night.
"We need to speak to anyone who saw the attack or the man running away.
"Any information at all that you have could be useful so please contact us."
Anyone with information should email firstname.lastname@example.org quoting serial 561 of 11/08, call 101 or contact the independent charity Crimestoppers anonymously on 0800 555111.