Police sealed off an area of grassland after a man was found with serious head injuries.
They believe the man, who yesterday was in a "critical" condition, suffered his injuries accidentally in an earlier fall.
The 57-year-old man had been taken to hospital after the fall and left prematurely before he could be treated.
The man, from the Whinmoor area of Leeds, had been to a local pub on Saturday evening and had fallen outside. An ambulance had been called and the injured man was taken to St James's Hospital, Leeds.
He was waiting to be seen by doctors when he apparently left the hospital of his own accord, said a spokesman for North East Leeds CID.
It is suspected the man may have set off to walk from the hospital towards his home in Whinmoor but collapsed at the side of Oak Tree Drive between Amberton Road and Oakwood Lane.
He was detained in the Intensive Care Unit at the hospital.