Striker Mario Balotelli complained about being subjected to abuse first, with midfielder Yaya Toure backing up his claim, leading to City informing the delegate of their plans to complain. Although manager Roberto Mancini did not hear the abuse, Balotelli has told a club official he heard abusive chanting during the game at the Estadio do Drago, which City won 2-1.
Reports circulated during the match that Balotelli and Toure were subjected to monkey noises. But when asked about it, Mancini said: "I didn't hear this because I was concentrating on the game. I don't know if (it happened) to Mario and Yaya."
When asked if either player had mentioned it to him, he said: "No."
Toure, speaking to Sky Sports News, confirmed he had "heard something" from the stands.
"That's why we all like the Premier League, because it never happens there," he said. "Maybe in foreign countries they don't expect black players.
"I think in future it will be okay, they will change their minds and the game will become more open. Football is football and the fans come to enjoy the game, and we don't want things like this to happen."
Balotelli told a club official he heard abusive chanting, leading to the complaint.
Otherwise, Mancini hailed his "fantastic" players after they came from behind to take the advantage after the first leg of the last-32 tie, Sergio Aguero coming off the bench to score the winner six minutes from time after an Alvaro Pereira own goal had cancelled out a Silvestre Varela strike.
Mancini said: "I think it was a good result because it is difficult to win here. I think we won this game because we played very well and didn't give more chances to score to them. I think the guys were fantastic."