Officers are appealing for witnesses and footage after a collision involving a car and a pedestrian in Haywards Heath.
Emergency services attended the scene on the A272 Lewes Road, near the junction with Hurstwood Lane, at about 10.10am on December 19.
An 80-year-old man sustained serious injuries and was taken to the Princess Royal Hospital in Haywards Heath, where he remains.
Police want anyone who may have witnessed what happened, or anyone in the area with relevant CCTV or dashcam footage, to come forward.
Information can be reported to Sussex Police online or via 101, or email: email@example.com and quote serial 305 of 19/12.