A 19-year-old man has been arrested on suspicion of assault in connection with an incident in Kingsbury Square, Aylesbury.
The incident occurred at around 10:20pm on Wednesday (11/7) when a 30-year-old man was punched in the head, knocking him unconscious.
The victim fell to the ground and hit his head on the concrete.
He was taken to Stoke Mandeville Hospital with life threatening head injuries. He was then transferred to John Radcliffe Hospital where he is currently in a serious but stable condition.
A man, aged 19, from Aylesbury, has been arrested on suspicion of assault and released under investigation.
Anyone who may have seen anything is asked to call 101 quoting reference number 43180211337 or call Crimestoppers anonymously on 0800 555 111.