A 45-year-old man is critically ill in hospital with serious head injuries after apparently being assaulted on Tuesday morning in Ardglass.
The PSNI say that the man is thought to have been kicked in the head by another man.
The incident happened at Strangford Road just before 11am.
A 23-year-old man was arrested in relation to the incident shortly after.
He has since been released on bail pending further police enquiries into the incident.
Police have appealed for witnesses who may have been in the Strangford Road area at the time to contact them.