The collision took place on the A259, Albion Street, at the junction with Station Road in Southwick on Friday, July 7.
Though the crash happened at around 10.25pm, the road was closed until 1am for recovery while police investigated.
A spokesman for Sussex Police: “Emergency services attended and the motorcyclist, a man aged in his 20s, was taken to hospital with serious injuries.
“Officers are investigating and are particularly looking to identify anyone that was travelling on the A259 between Hove and Shoreham at that time and may have seen the motorcyclist prior to the collision.
“Anyone with any information or relevant dashcam footage is asked to email firstname.lastname@example.org quoting 1771 of 07/07.”