A man suspected of being involved in a burglary at Grafton Street in Brighton was found on the first floor of the property by police with serious injuries.
The 35-year-old man from Brighton was treated at the scene by paramedics and taken to Royal Sussex County Hospital.
Three other people have been arrested on suspicion of burglary, which took place at around 12.40am on Saturday 2nd April.
A 35-year-old man, a 21-year-old woman and a 17-year-old girl, all from Brighton have since been released on bail pending further enquiries until Friday 27th May.
A fourth suspect, a 35-year-old man from Brighton, was found by police on the first floor needing medical attention. He was treated by paramedics and taken to the Royal Sussex County Hospital, Brighton, with serious injuries.
Anyone with information is asked to contact Sussex Police on 0845 60 70 999 quoting serial 65/2 or to the independent charity Crimestoppers on 0800 555 111.