Police were called at about 9am on Thursday, May 12 to reports of a collision involving a moped and a pedestrian in Kennington Lane at the junction with Kennington Road.
Officers and the London Ambulance Service attended. The 82-year-old pedestrian was taken to a South London hospital with a serious head injury. His family has been informed.
The rider stopped at the scene and has spoken with police. There has been no arrest.
Officers from the Serious Collision Investigation Unit based at Catford would like to speak with any witnesses who are yet to speak with police or anyone with dash cam footage. They are asked to call officers on 020 8285 1574.