We're trying to find out what happened after a car left the road and overturned, seriously injuring the driver, on the B2112 New Road at Clayton, south of Hassocks, in the early hours of Saturday (9 February).
The casualty was a 55-year-old man from Portslade-by-Sea. His black Suzuki sports utility vehicle had been travelling towards the A273 Brighton Road when the crash happened, leaving him with multiple injuries.
The Kent, Surrey and Sussex air ambulance attended, but he was taken by road to the Royal Sussex County Hospital, Brighton, where he is currently being treated.
There were no other casualties. The crash happened shortly before 1am. Local road closures were put in place until 7am while the incident was being dealt with.
Anyone who saw what happened, who may have dash-cam footage or other relevant information is asked to contact police online or by phoning 101, quoting Operation Ross.