A man had his throat and chin cut while sitting in a stationary car in North Lincolnshire, police have said.
The driver, 28, was sitting in the silver Peugeot 307 on George Street, in Scunthorpe, at about 0055 GMT on 13 February when he was approached.
A man allegedly opened the driver's door and cut the victim's chin and throat with a sharp blade before leaving.
Humberside Police said the motive for the assault was unclear.
Officers have conducted house to house inquiries and checked CCTV footage.
Anyone with information is urged to contact police.