An 18-year-old man who was found in a park off Hollow Way and Wilkins Road in Cowley with head injuries is in a stable condition at the John Radcliffe Hospital.
Police were alerted shortly after 4am on Sunday.
Det Sgt Roger Lamboll, of St Aldates CID, said: “The man’s condition has improved but we continue to investigate whether or not this man has been assaulted and how he has sustained his injuries.
“We are keen to speak to anyone who has any information about what happened and would ask them to contact us urgently.”
Anyone with any information should contact Det Sgt Lamboll via 0845 8 505 505.
Alternatively, please call the Crimestoppers charity anonymously on 0800 555 111.
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