A 25-year-old man was found with serious head injuries in his Horsham flat yesterday (Sunday August 18).
Emergency services including an air ambulance were called to North Parade just before 1pm.
He was taken to St George’s Hospital in south London for treatment.
A spokesperson for Sussex Air Ambulance said the service responded to reports of an assault.
But Sussex Police are trying to establish what happened.
A force spokesperson said: “Police are currently carrying out enquiries in order to establish the full circumstances and it is not yet clear how the man came by his injuries.”