At around 7.40pm on Friday April 17 the motorbike and a car crashed at the junction of High Street and Spa Lane near the railway crossing.
The incident involved a black 125 cc Pulse motorcycle which was travelling towards Harrogate from Knaresborough, and a red Skoda Fabia.
North Yorkshire Police are now appealing for witnesses.
Traffic Constable Ken Riley said: “There were a number of people in the area around the time of the incident, both witnesses and those who stopped to help the motorcyclist, who have not yet spoken to the police. They may have vital information which could assist our investigation.
“I would urge anyone who may be able to help establish the circumstances leading up to the serious injuries to the rider to contact me as soon as they can.”
Anyone with information is asked to contact North Yorkshire Police on 101, select option 2 and ask for Traffic Constable 1656 Ken Riley or email [email protected]
Please quote reference number 12150063086 when passing on information.