An Irchester man was left with serious injuries after his car left the road between Wollaston and Bozeat.
The 26-year-old was driving his Citroen Saxo along the A509 just after 8.30pm on Sunday, May 18, when his vehicle left the road and ended up in a ditch.
He has since been taken to University Hospitals Coventry and Warwickshire for treatment.
Officers investigating the incident do not yet know why the vehicle left the road.
Witnesses or anyone with any information about this incident can call the police on 101 or the Drivewatch Hotline on 0800 174615.