A man was taken to hospital after he was assaulted in Kingsbury in the early hours of Saturday morning.
The 26-year-old was found near Ladbrokes at 2.40am by members of the public and police.
Officers are now appealing for witnesses, and the man remains in a serious but stable condition.
Det Sgt Robert Ducker, investigating the incident, said: “The man was found in the town by members of the public and although we are in the early stages of the investigation our enquiries lead us to believe that this man has been assaulted.
“I would urge anyone who witnessed what happened and has not yet spoken to a police officer or was in the area at the time and saw the man before he was assaulted, to come forward.”
Call police on 101.
> The original description of the victim, as given by the police, has now changed.