It occurred on St Helen’s Road at the junction with Tadcaster Road in Dringhouses, York, at around 4.45pm on Monday as the gritter prepared for Storm Barra.
The rider, who is aged in his late teens, had to be freed from underneath the gritting lorry by firefighters while receiving emergency treatment from paramedics.
He was taken to hospital by ambulance with suspected serious lower body injuries.
The driver of the gritter, a man aged in his 40s from the Selby area, was not injured in the incident. He is helping the police with the ongoing investigation.
Local diversions were in place while the emergency services worked at the scene.
The roads reopened just after 6pm.
Witnesses, motorists with dashcams or anyone who recalls seeing the cyclist or the gritter prior to the incident, are urged to contact North Yorkshire Police on 101, select option 1, and speak to the Force Control Room. Alternatively, you can make a report via the North Yorkshire Police website. Please quote reference number 12210255965 when providing details.