A driver fell unconscious after he was punched at a set of traffic lights.
Police say a fight broke out on the A10 Great Cambridge Road between two groups of men on the afternoon of March 1.
Between 3.30pm and 4pm, they were seen arguing near Pasteur Gardens, just south of the North Circular junction.
The dispute involved people in two cars and the driver of one of the vehicles punched the other driver in the face.
He fell to the ground falling unconscious before being taken to hospital with serious injuries.
The Met says the man, in his 30s, continues to receive medical treatment.
Police say the suspects were not at the scene when officers and paramedics were called.
The victim was travelling in a Vauxhall Zafira while enquiries are ongoing to trace the make and model of the attacker's vehicle, police added.
Detectives are investigating the road rage incident and are appealing for witnesses.
Detective Constable Jonathan Powley said: "We believe that the drivers were involved in a verbal dispute, which turned into a nasty road rage incident where the victim was knocked unconscious in an unacceptable act of violence.
"We are keen to speak to any witnesses who have not yet come forward to the police. Maybe you captured the incident on your dash cam or mobile phone?
"Do you have a description of the suspects? Did you see the number plate of the suspects’ vehicle? Any information you have, no matter how small, will help us with our investigation."
Anyone with information or footage is asked to call police on 101 or Tweet @MetCC quoting CAD 4650/01MAR.
Alternatively, contact Crimestoppers anonymously on 0800 555 111 or online at crimestoppers-uk.org.
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