Detectives in Sheffield have released CCTV images of a group of people believed to hold information about a city centre attack.
A 22-year-old man suffered a serious head injury when he was attacked on Milton Street after he and a group of friends were approached by another group.
He told police one member of the other group lashed out at him - punching him to the ground.
The attacker was a muscular man with short dark hair and a trimmed beard.
He was around 5ft 10ins tall and was wearing a red T-shirt with black wording on it. He is also believed to have a tattoo on the right side of his neck.
A South Yorkshire Police spokeswoman said: “At around 3.30am on Saturday, May 12, it is reported that a 22-year-old man was walking along Milton Street with a group of friends, when another group of men approached them.
“It is alleged that one of the men in this group assaulted the 22-year-old, punching him to the floor. The 22-year-old was taken to hospital to be treated for a serious head injury.
Investigating officers have released CCTV images of a group of people they believe may hold information.”