Roads and Transport Policing officers are appealing for witnesses to a road traffic collision in Wandsworth on Sunday, 20 November.
Police were called at around 03.35hrs that day to reports of a collision involving a motorcycle and a BMW X5 in Totterdown Street, near the junction with Franciscan Road, SW17.
The rider, a 19-year-old male, is currently in intensive care with a bleed on the brain.
Detectives from the Serious Collision Investigation Unit are carrying out enquiries into the circumstances of the collision.
At this early stage it is believed the rider was travelling south along Franciscan Road when the BMW, travelling north, turned right into Totterdown Street. The two vehicles were then in collision with each other.
The driver of the BMW, a 22-year-old man, left the scene prior to police arrival. He was later located and arrested on suspicion of drink driving and failing to stop at the scene of a road traffic collision.
He was taken to a south London police for questioning before being bailed to a date in late January.
Any witnesses or anyone with any information are asked to call the Serious Collision Investigation Unit on 020 8543 5157.