Stonnington Crime Investigation Unit detectives are investigating an assault and robbery in South Yarra.

Detectives have been told a male victim had been out at a licenced premises on Chapel St in Prahran.

The man was befriended by an unknown female at the licenced venue, and both left together about 3.20am on November 25.

They were followed to nearby Bray St in South Yarra by two males that arrived at the bar with the female.

The two males and the female then assaulted the victim, punching him, leaving him with bruising.

The offenders also stole a small quantity of cash from him before leaving on foot.

The first male is perceived to be Caucasian, described as approximately 30-years-old with a thin build, dark hair and facial stubble and was wearing a black baseball cap, black zip up jumper with white bands around the left arm, grey tracksuit pants and black Nike trainers.

The second male is described as approximately 30-years-old, perceived to be Caucasian with a medium build and was wearing black baseball cap with white LA logo on the front, black Kappa tracksuit with white stripe down the arm and leg and green trainers.

The female is perceived to be Caucasian, approximately 25-35-years-old with a thin build and long brown/blonde hair and was wearing a black zip up jacket with white text down the right sleeve, blue skinny jeans, or jeggings.