Gardaí at Coolock are seeking help from the public following an incident in which a man sustained serious head injuries.
The 41-year-old from Ballymun was in Darndale Park, north Dublin, yesterday afternoon while work was being carried out on his car.
The man fell asleep in the afternoon sun and was later found badly injured.
Investigating gardai said the man doesn't remember what happened to him.
One line of inquiry is that he may have been struck by something while asleep.
Detectives believe children were riding at quad bike in the park around the time of the incident, after 2.30pm.
Gardaí are seeking witnesses to the incident.