Police were called at 12:08pm on Saturday, 22 June, to a collision involving a motorcycle and car on Hayes Lane in Kenley, close to the aerodrome.
Officers attended along with the London Ambulance.
The male rider of the motorcycle was taken to a south London hospital where he remains in a critical condition.
The driver of the car stopped at the scene. There have been no arrests and enquiries continue.
Officers from the Roads and Transport Policing Command are investigating.
They would like to speak with anyone who was in the area at the time, or any motorists who may have captured the collision on dash cam.
Anyone with information is asked to call the Serious Collision Investigation Unit on 020 8285 1574.