A football player is described as being in a critical condition after a late night assault.
The victim is Niall Grace, a member of Institute FC, based in south-east Londonderry.
At time of writing he was in the Royal Victoria Hospital in Belfast, having been transferred there from Londonderry.
It is understood that he is originally from the western side of Londonderry, and that he is aged either 23 or 24.
He had joined the first team around 10 months ago, and is a centre midfielder for the club, which currently plays in the Championship 1 league (the next one down from the premiership).
The club had just beaten PSNI FC 4-0 on Saturday.
It is believed that Mr Grace is unmarried, but has a girlfriend.
The precise circumstances of what happened are not yet known.
Detectives said they were appealing for witnesses and information about what they described as a “serious assault”.
It took place at approximately 12.45am on Sunday in Waterloo Street in the city centre.
He was initially described by the police as being in a critical state, and when the News Letter spoke to the Belfast Health Trust on Sunday night, this remained unchanged.
Police said a 22-year-old man was arrested a short time after the incident.
Detective Constable Stephen Riddell said: “We are conducting inquiries and are requesting the public’s assistance to help determine the full circumstances surrounding the incident.”
He asked anyone with information to call 101, quoting reference number 78 of 11/09/16, or call Crimestoppers anonymously.