A man suffered four fractures when his arm was stamped on outside a restaurant.
The victim and his partner were believed to have been in an altercation with four men outside Dantes at the Halfway House, on Preston Road, Clayton-le-Woods, early on Sunday morning.
It is thought he was pushed to the ground by one of the men, who then stamped on his arm.
Police said the 32-year-old man suffered four fractures to his arm and wrist, which will require extensive hospital treatment.
The incident happened between 1.05am and 1.20am, shortly after the bar and restaurant had closed.
The attacker was described as white, around 5ft 10ins to 6ft tall, of a medium build, with short dark hair and a chiselled jaw.
He wore a black T-shirt and dark denim jeans and was seen leaving in a white taxi.
PC Emma Collins, of Chorley police, said: “This was a nasty attack leaving the victim with multiple fractures.
“We are appealing for anyone who may have witnessed the incident, or anyone who may have information that could help us with our enquiries, to get in touch with us on 101 quoting SC1400549.”
Alternatively, contact Crimestoppers, anonymously, on 0800 555 111 or at Crimestoppers-uk.org.