The incident happened on Garnet Street, near Sauchiehall Street, between 1.55am and 2.15am on Tuesday.
The man was approached by two other men who subsequently assaulted him.
He was taken to Glasgow Royal Infirmary for treatment to serious but non-life threatening injuries.
One of the two men is described as white, about 5ft 10in tall with short dark hair. He was wearing a blue North Face jacket with black shoulder pads, black trousers and spoke with a Glasgow accent.
The second man is described as being white, around 6ft tall, with dirty blond hair, a beard cut short at the sides and long in the middle and dark clothing.
Detective Constable Larissa Cooper said: “This assault was entirely unprovoked and we are working to identify the other two men involved.
“If you have were in the area and saw or heard the incident, or have any other information please come forward.
“You can pass on information by calling police on 101, quoting reference 0226 of 12 April, or call Crimestoppers anonymously on 0800 555 111.”