A 22-year-old man is critically ill in hospital with head injuries after being attacked in Nottingham city centre.
The attack happened near the Bla Bla Bar in James Street at about 2345 BST on Friday.
Police believe the victim was involved in an altercation and ejected from the bar shortly before being attacked.
Officers said they would like to speak a man described as mixed race, slim, about 5ft 10in tall, who may have been in the company of up to three women.
The injured man was taken to Nottingham's Queen's Medical Centre, police said.
The scene of the attack was sealed off for forensic checks but the cordon has since been lifted.
Det Insp Leigh Sanders said: "This attack would have been witnessed by a number of people including bar staff and customers.
"It was also captured on CCTV and we believe it is only a matter of time before the identity of the person who carried out the attack is known.
"We urgently want to speak to anybody who witnessed the attack."