A 22-year-old man was arrested at his home in north London over the killing of David Forbes, 42, from Dundee, and is in custody at a north London police station.
Forbes fell to the ground after being punched by a man outside The Rocket pub on Euston Road, central London, at about 2.25am on November 25.
A Metropolitan Police spokesman said Forbes was being treated for a head injury but was pronounced dead last night.
His next of kin have been informed and a post-mortem examination is due to be held. Officers from the Homicide and Serious Crime Command are investigating the incident.