Wiltshire Police is appealing for witnesses to an incident which occurred on the A361 between Beckhampton and Devizes.
The incident happened at approximately 4pm on 14 March.
A man in his 50s was driving a silver Nissan Leaf towards Beckhampton from Devizes when, approximately 1km from the Beckhampton roundabout, the driver was struck in the head by a metal hook which smashed through his front windscreen.
He sustained a laceration to his head and was taken to the Great Western Hospital by land ambulance.
PC Ben Cox, of the Roads Policing Unit, said: “It is not known if this hook came from another vehicle, or if it has been thrown up from the carriageway by another vehicle, and into the windscreen of the victim’s car.
“We’d like to hear from anyone who may have been driving along this stretch of road around this time, especially anyone who may have dash cam footage.”
Anyone who can help the investigation should call police on 101 or Crimestoppers anonymously on 0800 555 111.