He was in a critical condition at the Mid-Western Regional Hospital.
The man was found unconscious in the basement of a house in Catherine Street at about 3.30am on Saturday.
He is understood to have fallen about 12 feet from a ground floor window and received head injuries.
The house has been vacant for some time and was frequently used by street drinkers late at night.
Supt Frank O’Brien said: “It appears he may have entered the house through an open window. And when he was leaving, he went to another window which opened on to the outside basement. It would seem he was not aware that there was a drop into the basement outside this window.”