The crash happened at around 4pm on May 13 near Willerby and police are now appealing for information and witnesses.
North Yorkshire Police said a red tractor and a black Yamaha motorcycle, both of which were travelling away from Willerby towards Malton, were involved.
The biker ,a 40-year-old man, was taken to hospital with life-threatening injuries, while the driver of the tractor, a 58-year-old man, was not injured.
The road was closed for more than six hours as police carried out investigations and recovered the two vehicles.
Traffic Constable Mark Patterson, of North Yorkshire Police’s roads policing group, said: “We would like to speak to anyone who saw either vehicle prior to the collision or who witnessed the collision who has not already been spoken to by police, particularly if they have dashcam footage.”
Anyone with information is asked to call police on 101, email TC Patterson on [email protected] and quote incident reference number 12210117308.