UEFA president Michel Platini has ordered an investigation after a Champions League referee failed to follow guidelines and stop a match to warn Russian fans about racist abuse.
UEFA says its protocol for racism incidents "was not applied" during the CSKA Moscow-Manchester City match Wednesday.
UEFA has opened a disciplinary case against CSKA, prompted by complaints by Man City and Ivorian midfielder Yaya Toure.
Toure said he told Romanian referee Ovidiu Hategan during play about monkey noises being targeted at him by home fans.
Hategan did not stop play and ask stadium officials to broadcast a warning, the first step of UEFA's guidelines to deal with racist abuse.