The 28-year-old victim reported being approached by an unknown man outside the Post Office in Portland Road at around 11pm on September 25th, 2021, police said.
He was then assaulted, causing facial injuries that required hospital treatment, they added.
Police said the suspect made off west along Portland Road.
A Sussex Police spokesperson said: “The incident was captured on CCTV and officers would like to speak to anybody who recognises the man in the footage or has any information that could help with the investigation.”
People can contact police online via the Sussex Police website, or by calling 101 and quoting serial 1041 of 27/09.