The driver was injured after his vehicle left the road on the main Muff to Moville road at the Quigley’s Point turn-off for Carn.
Gardai say no other vehicles were involved in the crash.
Ambulance crews were called to the scene around 4pm.
The motorist was taken to Letterkenny for treatment for a number of injuries.
The road has been closed off while Gardai carry out a follow-up examination of the scene.
The incident comes two days after a Moville man died in a crash just outside the town.