Man has jaw smashed in street attack
The 46-year-old victim, who police said suffered from "underlying medical issues", was approached by a man outside the Jazz Bar on Chambers Street at 12.30am on Friday.
The suspect tried to engage the victim in conversation before he punched him, leaving him with a fractured jaw which needed treatment at Edinburgh Royal Infirmary.
The attacker made off along Chambers Street and turned left on to South Bridge heading towards Princes Street.
The suspect is described as being white, 35 to 45 years old with shoulder-length brown hair which was swept back. He was clean shaven, spoke with a local accent and wore a grey suit jacket and grey trousers with a white shirt.
A police spokesman said: "We know the area would have been busy at the time and it's unlikely this kind of incident would have gone unnoticed."