The incident happened at around 12:20am today when the 39-year-old was approached by the gang of three men and two women near Nicolson Street in Edinburgh city centre.
He had left a Tesco store and turned on to Gibbs Entry when the group asked for money and cigarettes. The man offered them cigarettes but was assaulted in an apparently unprovoked attack, police said.
They then stole cash and cigarettes as he lay on the ground.
The men are described as mid-to-late 30s. One was wearing a white jacket, the other a grey top with shoulder patches, and the third was wearing an olive green jacket.
The two women are described as mid-to-late 20s. One was wearing a black Adidas top and the other was wearing tracksuit top which was mainly pink.
Pc Kevin Walls said: “We are pursuing a number of lines of inquiry in relation to this incident but I would ask anyone who was in the area of Nicolson Street around the time of this crime and who has information that can assist with our investigation to please get in touch.
“It appears this was a completely unprovoked and vicious assault with the suspects showing absolutely no regard for the welfare of the victim.
“Officers are now reviewing local CCTV footage and speaking with members of the local community in an effort to trace those responsible.”