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Manchester City have been reported to UEFA over their fans' continued booing of the Champions League anthem, Press Association Sport understands.
Disciplinary proceedings will now be opened by the European governing body and a charge could follow if it is deemed the club have a case to answer.
It is understood the matter was reported by a match delegate after the anthem was jeered by home fans prior to City's Champions League victory over Sevilla at the Etihad Stadium on Wednesday.
UEFA is now obliged to consider the matter but this is standard procedure and it does not necessarily mean the club will be hit by sanctions. City have not commented following the development.
City fans have regularly booed the Champions League anthem over the past year in protest at the financial fair play punishment meted out to the club by UEFA in 2014.
City were fined ?49million, hit with a transfer spending cap of the same amount and forced to limit their Champions League squad last season to 21 players rather than the regular 25.
Their disgruntlement with UEFA grew when a match against CSKA Moscow in the Russian capital last October was ordered to be played behind closed doors because of the behaviour of home fans. A number of City fans had already paid for tickets, travel and accommodation and felt they were being unfairly punished.
An organised boycott of the anthem was arranged in conjunction with Bayern Munich fans, who had a similar issue over a game in Moscow, prior to a game against the Germans last December. Both sets of supporters turned their backs during the anthem.
City manager Manuel Pellegrini this week refused to criticise supporters over the matter.
The Chilean was asked before the Sevilla game if the continued booing might be affecting his players in creating a negative atmosphere before games.
Pellegrini said: "I think we always have in the Etihad the atmosphere we need in Champions League, Capital One Cup or Premier League. We always feel the fans are behind the team and they always support us a lot.
"I don't think the atmosphere is lower than what we need. It is a good atmosphere."