A Northampton town centre alleyway was closed off by police on Saturday after a man was punched in the head and knocked unconscious.
Police are appealing for information after the assault in the Drapery, Northampton, left a man with a serious head injury.
The incident happened close to an alleyway near McDonalds between 5.10am and 5.15am on Saturday, February 9. The victim was punched once to the head, causing him to lose consciousness and collapse. He remains in hospital in a serious but stable condition.
Officers investigating the incident would like to speak to group of white men in their late teens or early 20s, who were wearing dark clothing, who were in the area at the time.
A 19-year-old Northampton man arrested on suspicion of grievous bodily harm has been released under investigation.
Anyone with information or who witnessed the incident is asked to call Northamptonshire Police on 101. Information can also be shared anonymously via Crimestoppers on 0800 555111.