A 20-year-old student was assaulted in Lancaster city centre in the early hours of Friday, February 1.
The victim was stood with friends on Horseshow corner around 3.15am when a man from another group punched him in the face causing him to sustain a fractured jaw.
DC David Winn said: “An investigation is underway but I would appeal to anybody who witnessed this assault to come forward and contact Lancashire Police on 101.”
The attacker is described as being white, slim build, around 5ft 10inches tall with ginger hair. He was wearing a blue chequered shirt and spoke with a local accent.
Contact Crimestoppers anonymously on 0800 555 111 or online at Crimestoppers-uk.org.