Greater Manchester police made four arrests after crowd trouble at Old Trafford on Thursday night.
The force said that while most of the 3600 Real Betis fans in the stands for the Manchester United Europa League match were well-behaved, around 50 engaged in ‘disorder’ towards home fans, stewards and police officers during the game.
Police said throughout the fixture, a number of flares and pyrotechnics were used inside the stadium by Real Betis supporters and objects thrown across the supporter segregation lines, during which a police officer was injured as a result of a pyrotechnic being thrown by a person in the away section.
Four Real Betis supporters were arrested for violent disorder, assault, possession of flare inside the stadium and possession of controlled drug. Two of them currently remain in police custody for questioning on Friday.
Chief Inspector Jamie Collins, said: “The violent disorder experienced does not reflect the majority of supporters attending this fixture who went just to watch the football on the pitch.
“Last night’s behaviour by the minority was totally unacceptable and quite shocking for the decent supporters who may have got caught up in this.
“We are also continuing to offer the welfare needed to support one of our colleagues who was injured as a result when trying to keep the public safe.
“GMP are working closely with Manchester United, the UK Football Policing Unit, Real Betis, UEFA and Spanish Police colleagues to identify those involved in a post-match investigation which is ongoing.
"If any supporters from Manchester United or Real Betis and those attending the game have any information or footage that can assist with enquiries, they are asked to contact Greater Manchester Police on 101 as soon as possible so we can bring those responsible to justice and also to seek, where possible, football banning orders."