The incident took place at the junction of John Street and the Manor at around 3am.
The man, who received head injuries, was taken by ambulance to University Hospital Waterford and subsequently transferred to Cork University Hospital where his condition is described as serious.
Anyone with information should contact Waterford Garda station on 051-305300, the Garda Confidential Line on 1800 666 111 or any Garda station.
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