A 34-year-old man is seriously ill in hospital after he was attacked in York in the early hours of New Year's Day.
North Yorkshire Police said the man suffered a head injury when he was assaulted on the city's Hungate at about 0350 GMT.
He is in a serious condition at York District Hospital.
A 30-year-old man was arrested over the incident and is being questioned by police. A force spokesman appealed for witnesses to come forward.