Anyone who witnessed or has dashcam footage of a serious collision between a car and motorcycle in Cuckfield Road, Ansty, on Tuesday, August 30 is asked to report it to police.
The collision happened around 9.45pm which involved a silver Volkswagen and a blue Honda motorcycle and resulted in the road being closed for several hours while emergency services attended the scene.
An 18-year-old man who was riding the motorcycle was taken to Royal Sussex County Hospital by air ambulance with serious, life threatening injuries.
If you have information or dashcam footage which could help officers with their investigation email collision.appeal@sussex.police.uk or call 101 quoting Operation Wickford.