Manchester City's Michael Johnson is under investigation after allegedly headbutting a fan of rivals United in a nightclub, police have confirmed.
A fracas erupted after the alleged victim was singing Manchester United songs with friends in the club, 42nd Street, in the city centre.
Johnson, 22, tipped as a Premier League star of the future and who has represented England at Under 21 level, was arrested later and interviewed by police. He is currently on bail.
The alleged victim, 22, is understood to have flagged down a passing police patrol in the early hours of 6th December, last year.
Johnson was later approached by police and an appointment was made for him to attend a police station to be questioned over the incident.
He was arrested on suspicion of assault causing actual bodily harm and has been bailed until 14th April.
The midfielder came through the ranks at the club's academy and captained their FA Youth Cup team before making his first team debut in October 2006.
He has also represented England at Under 19s and U21 level but has been dogged by injury in the last two seasons and is currently out of action with a knee injury.
A spokesman for Greater Manchester Police said: "Just after 1am on Sunday 6 December 2009, a patrol car was flagged down and an officer was told a man had been assaulted.
"The 22-year-old victim reported that he had been assaulted in 42nd Street nightclub. The man had a cut to the face but no other injuries.
"A 22-year-old man has been arrested on suspicion of causing actual bodily harm, a section 47 assault, and remains on police bail until 14 April 2010 as inquiries continue.
"Two other men, aged 21 and 22, have been interviewed under caution to assist inquiries."