A man required hospital treatment following an assault in the centre of Brighton on Sunday morning.
The 32-year-old victim, who is from London, had money stolen from him during the attack which saw him suffer facial injuries.
The assault took place at 9.45am at Russell Square, which is a short distance from Churchill Square.
Detective Sergeant Julie Greenwood of Brighton and Hove CID said: “We believe this is a dispute between two people who are known to each other.
“We would like to hear from anyone who may have seen anything the offence taking place in the street.”
Anyone with information is asked to contact Sussex Police on 0845 60 70 999 quoting serial 552 of 4/9 or the independent charity Crimestoppers anonymously on 0800 555 111.