A man is in intensive care in hospital following an incident in Willowherb Road in Lyde Green in the early hours of today.
Police were called at 1.42am to a report of a man having been detained by a member of the public after allegedly trying to break into cars.
Officers attended by 1.51am and found the man to be unresponsive. An ambulance arrived at 2.05am and the man was taken to hospital where he remains in intensive care.
Earlier today police issued an appeal to identify this man but later said they believe they know who he is.
A 35-year-old man has been arrested on suspicion of GBH and remains in police custody this morning. Inquiries are ongoing.
Anyone with information about the incident who has not yet spoken with officers can get in touch through www.avonandsomerset.police.uk/contact or by calling 101, quoting reference 5219628280.