It happened last year according to this.
City star Michael Johnson arrested over headbutt claims
Exclusive by Mike Keegan
March 03, 2010
Manchester City star Michael Johnson has been arrested by police investigating claims that a United fan was headbutted in a nightclub.
The 22-year-old midfielder was interviewed after the Reds' supporter complained that he had been attacked in 42nd Street, a nightclub on Bootle St, Manchester, which is popular with students.
Greater Manchester Police approached City after the complaint was received and arranged an appointment for Johnson to attend Grey Mare Lane station, yards from the club's Eastlands stadium.
He was arrested on suspicion of assault causing actual bodily harm and has been bailed until March 18.
Johnson, who is from Urmston and came through the ranks at the City academy, ruptured his knee ligaments in training on December 10.
The club's then manager Mark Hughes announced that he could be out of action for the rest of the season.
The alleged assault happened four days earlier.
It is understood a group of United fans in the nightclub began singing popular Old Trafford songs and one of them approached Johnson.
Kicked
The Reds fan, 22, claims that he was then headbutted, knocked to the ground and kicked while he was down.
The supporter left the nightclub and flagged down a police officer to report the alleged assault.
Johnson burst into the limelight as a teenager in 2006 after making his debut against Wigan and was tipped for Premier League stardom.
He has suffered a number of injury setbacks but has played 37 times for the Blues and scored two goals.
This season he made a comeback, scoring in October's Carling Cup victory over Scunthorpe.
Johnson has not played since the injury in December. The club said the injury was sustained on the training ground and was completely unrelated to the nightclub incident.
A spokesman for GMP 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 reported that he had been assaulted in 42nd Street nightclub.
“He had a cut to the face but no other injuries.
“A 21-year-old man has been arrested on suspicion of causing actual bodily harm and remains on police bail as inquiries continue.”
Two other men are also under investigation but have not been arrested.
The maximum sentence for actual bodily harm (section 47 assault) is five years imprisonment.