The 33-year-old was found in Redbridge Hollow, off Abingdon Road on Saturday Morning.
Officers were called by South Central Ambulance Service just before midday on Saturday to reports of a man being unresponsive at his home, he was then pronounced dead at the scene.
A Home Office post-mortem examination concluded he had died as a result of a head injury.
A 30-year-old man from Oxford has been arrested on suspicion of murder and currently remains in police custody.
Senior investigating officer Detective Chief Inspector Stuart Bosley, of Thames Valley Police’s Major Crime Unit, said: “This is a tragic incident where a man who has suffered a head injury, has very sadly passed away.
“Although we are in the very early stages of this investigation, we believe this followed an incident which occurred in the early hours of Saturday morning in Redbridge Hollow.
“The victim was unfortunately found deceased later the same morning.
“We have made an arrest in connection with this investigation, and I would like to re-assure the local community that we believe this incident to be isolated and that the victim and offender were known to each other.
“We are conducting a thorough investigation into the circumstances and we are supporting the victim’s family. Our thoughts are with them at this very difficult time, and we would ask that their privacy is respected.
“I can assure the community that we will leave no stone unturned to ascertain exactly what has led to the death of the victim.”