Police are appealing for witnesses after a yellow Vauxhall Corsa crashed into railings of the A406 North Circular Road.
The incident took place opposite Brent Cross Shopping Centre, at around 12.15am on Wednesday April 20.
The 25-year-old driver of the Corsa was injured and taken to hospital, but was later discharged.
Witnesses reported seeing a blue sports car - described as a McLaren - leaving the A406 at the Brent Cross Flyover just before the crash.
PC Oliver Martin from the roads and transport policing command, said: "We believe the driver of this car may be a significant material witness to the collision.
“It is unlikely they were aware of the collision, but we are keen to speak to the driver to see if they can assist our investigation."
Officers are appealing for the driver, or the owner, of the sports car to contact them.
Anyone with information can contact police via 101
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