Police were called to the eastbound A406 in NW10 at 04:59hrs on Friday, 14 August following reports of a road traffic collision.
Officers, London Ambulance Service and London Air Ambulance attended and found a lorry in collision with a pedestrian.
The male pedestrian was taken by London Air Ambulance to a central London hospital where he remains in a critical condition.
The driver of the lorry stopped at the scene and is assisting police with their enquiries.
No arrests have been made. Enquiries are ongoing.
The eastbound A406 in the area has now reopened.