A student suffered a double jaw fracture during an unprovoked attack outside a Great Harwood bar.
A group of unknown men approached the 20-year-old outside Snuffy’s bar on Snuffys Commercial Road.
Police said he was punched in the face and fell to the ground.
Detectives have released CCTV images of three men they want to speak to who they believe may be able to assist the investigation.
The incident happened on Sunday, March 23 between 2am and 2.30am.
Detective Constable David Gill from Blackburn CID said that earlier in the night, the victim and his girlfriend may have been involved in an altercation with the offenders.
He said: “I would appeal to anyone who was in the area at the time and who witnessed what happened to come forward and contact the police.
“It is also important that we track down the men in the CCTV. I would appeal to anyone who knows who these men are to get in touch or alternatively appeal to the men direct to speak to the police."
He added: “This was a nasty assault on a young man that left him with a fractured jaw and need hospital surgery. We need to get to the bottom of what happened.”
Anyone with information is asked to call Blackburn CID on 101.