A man who was found lying unconscious and with his jaw broken has told police he can remember nothing of the attack.
The victim was discovered in Moorgate Street, Mill Hill, Blackburn, Lancashire, early on Saturday and also had gashes to his head.
He was taken to hospital where he regained consciousness.
The incident happened shortly after he left a party in Hollin Bridge Street. Police want to hear from anyone who saw the man or heard a disturbance.
He is 28 years old and was wearing a distinctive blue and white striped jumper.
Police are carrying out house-to-house enquiries and have recovered what they believe may have been a weapon.