A teenager was slashed in the face with a Stanley knife in a Corby underpass in the early hours of Saturday morning (January 3).
The victim, 18, was attacked under Oakley Road, near Burghley Drive.
The man who attacked him is described as white, 5ft 10in tall, middle-aged and with blonde hair and a foreign accent.
He made off immediately after the incident.
Police would like to speak to anyone who may have witnessed this incident, which happened at some point between 4am and 6am.
Witnesses or anyone with information is asked to contact police on 101 or Crimestoppers anonymously on 0800 555 111.