Emergency services were called to a collision between a car and a motorcycle in Upper Shoreham Road, Shoreham, at around 7.35pm on Wednesday (21 June).
A Nissan Micra was reported to have collided with a Honda motorcycle at the Holmbush Roundabout.
The motorcycle rider – a man in his 60s – was taken to hospital with potentially life-changing injuries.
The driver of the car – a 36-year-old man from Brighton – was arrested on suspicion of causing serious injury by careless driving. He remains in custody at this time.
Anyone who witnessed the incident or has any relevant dashcam footage is asked to contact police online or via 101, quoting Operation Newbridge.