At around 11am on Saturday 17 May 17 a 64-year-old Seaford man riding a black Yamaha XVS motorcycle crashed into a water-filled ditch in Litlington Road, just north of its junction with the A259 East Dean Road at Exceat.
No other vehicle was involved.
The road was temporarily closed while emergency services dealt with the incident.
The motorcyclist suffered neck and leg injuries and was taken to the Royal Sussex County Hospital, Brighton, where he was detained for treatment.
The motorcyclist is in a serious but stable condition.
Anyone who saw what happened or who may have other information is asked to phone Sussex Police on 101.
Or witnesses can email firstname.lastname@example.org, quoting serial 629 of 17/5.