Police are trying to establish how the incident happened, after the man was found lying injured at the roadside in Kilmarnock at 10:30 last Friday.
He was taken to Crosshouse Hospital where he died later that day.
Police said they received a report of the incident on Monday and are asking anyone who was in the area at the time to get in touch.
Sgt Brian Simpson from Irvine Road Policing Unit said: “We are working to gather information that will assist us in establishing the circumstances.
“I would urge anyone who was in the area of Milton Drive on Friday morning to please contact us as soon as possible.”
