According to Sky Sports City squad were celebrating their 2-1 victory with loud music in an open-door dressing room when United staff took offence, and Mourinho is thought to have said something to those inside on the way to his post-match interviews.
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The former Chelsea and Real Madrid boss who was obviously not happy with the manner in which City celebrated their victory over United, said his side showed much respect to Arsenal after beating them 1-3 at the Emirates Sports Stadium
"For me it was just a question of diversity - diversity in behaviours and diversity in education. Just that and nothing more than that," Mourinho said.
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When asked to expand on what he meant, Mourinho continued: "Diversity of behaviour, of opinion, of education you know.
"What we did in the Arsenal stadium was completely diverse, what happened after that, the way we behaved as winners."
Mourinho was reluctant to speak about the fracas and grew more and more irritable as reporters persisted with the topic.