A motorcyclist was taken to hospital with serious injuries following a crash which may have involved another vehicle.
The collision happened at about 5.30pm on Wednesday April 6 when the motorcyclist, travelling westbound on the A422 near Steane Park, Brackley towards Banbury, came off the road into a ditch.
Northamptonshire Police say it is believed another vehicle was involved but did not stop following the collision.
The motorcyclist, a 45-year-old man from Banbury, was taken to University Hospital Coventry with serious injuries.
Investigators are appealing for witnesses and would particularly like to trace the driver of a yellow Seat Leon, which had a distinctive black and yellow chequered stripe across the bonnet and roof.
Witnesses to the collision or anyone with any information about the Seat Leon, is asked to call Northamptonshire Police on 101.