Police are appealing for witnesses to the assault outside the Rocket pub in Euston Road on November 25 at around 2.25am.
Witnesses saw the suspect punch the victim causing him to fall to the ground, striking his head on the road.
The suspect then walked off with a group of men and a woman towards King’s Cross.
The victim was rushed to hospital with a head injury and remains there in a critical condition.
Det Con Matt Burmby said: “This seems to have been an unprovoked attack, which has left a man seriously injured.”
The suspect is described as a white man, about 5ft 9inch tall and aged between 25-30 years. He is thought to have a muscular build with short dark hair wearing a plain white t-shirt.
Anyone with any information is asked to contact police on 101 or call anonymously on 0800 555 111.
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