Dorset Police are appealing for information after an elderly man was found lying on the A35 with serious injuries.
Officers believe the 79-year-old Bridport man had collided with a motor vehicle.
The man was found in the early hours of Sunday February 3 at Chideock Hill between Bridport and Lyme Regis.
Police Sergeant Jon Wren of Dorset Police's Traffic Unit said: "The injuries the victim sustained are very severe and are likely to seriously affect him for the rest of his life.
"Because of the time the incident occurred the motorist may have had the impression that an animal rather than a human was hit.
"I would therefore like to speak to anyone who has been in collision with anything and however small along this road during that night.
"I urge the driver in question to do the right thing and speak with the police.
"I am also appealing for witnesses to the collision as I need to establish exactly what happened."
Witnesses or anyone with information should contact Dorset Police on 101, quoting incident number 03:136.