The terrifying incident happened as the 24-year-old made his way home from a night out in the city centre.
He was approached by the suspect - who was wearing two jackets - and threatened with the blade.
The victim - who was forced to hand over his personal belongings - was walkingin George Street, when the fiend struck at around 4.45am on Saturday,
Police said CCTV footage showed the suspect speaking to another man in Georeg Street, near to Albion Street, at around 4.20am.
Officers believe he may be a witness and today urged him to come forward.
The robber is described as white, between 20 and 30-years-old, and around 5ft 10in tall.
Police said he has receeding dark hair and stubble. He was wearing a black puffa jacket with a hooded jacket over it.
Detective Constable John Johnstone, from the Community Investigations Unit, has appealed for witnesses to come forward.
Police have been reviewing CCTV footage and carrying out local inquiries in a bid to trace the man responsible.
A Police Scotland spokesman said: "We received a report of a robbery at around 4.45am on January 18 in George Street.
"A 24-year-old man was threatened with a weapon and forced to hand over personal belongings. Inquiries are ongoing and anyone with any information is asked to contact police."
Anyone with any information is asked to contact Pollok Police Office on 101.