North Yorkshire Police said the man in his late 20s was involved in collision with a white Renault HGV just after 5am today (Sat Dec 1).
He was taken by ambulance to James Cook Hospital in Middlesbrough where he is receiving treatment for serious injuries.
The collision happened on Leyburn Road, between Camp Centre and Plumer Road.
Diversions were put in place while the emergency services worked at the scene and to allow a full police examination.
The road reopened at around 10am.
Officers are appealing for any information that could assist the investigation, including possible sighting of the man or the white Renault heavy goods vehicle before the collision.
Call North Yorkshire Police 101, quoting reference NYP-01122018-0083.