At 8.50pm on Friday, December 24, a motor-cycle being ridden west was in collision with the 46-year-old male pedestrian in Brighton Road, Worthing.
Police said the pedestrian was taken to the Royal Sussex County Hospital in Brighton with serious head injuries.
Sussex Police added that the 21-year-old man riding the motorcycle sustained minor injuries and was arrested on suspicion of causing serious injury by dangerous driving, and drug driving. After being interviewed he was released under investigation.
PC Nick Halsey, of the Surrey and Sussex Road Policing Unit, said: “If you saw what happened we would like to hear from you. We would particularly like to speak to the driver of a Land Rover or Range Rover that was driving east at the time of the collision.
“If you can help please contact us on [email protected] or by calling 101, quoting Operation Cadder.”