Jose Mourinho is the subject of a complaint by a gay rights group after he allegedly used a Spanish homophobic insult about match officials.
The Real Madrid manager has been accused by the European Gay and Lesbian Sports Federation (EGLSF) of referring to officials as "maricones", which translates as "faggots" in English, before the Champion's League tie against CSKA Moscow.
Louise Englefield, co-president of the EGLSF, called on UEFA to take action over the comments, which were shown on the Spanish television channel Quatro.
She said: "Homophobia is unacceptable from anyone in football, much less from one of the game's most senior figures. We are deeply disappointed that Mr Mourinho is casually using homophobic terms of abuse in his workplace.
"It is especially sad that these comments have been made during the International Football v Homophobia campaign week.
"As long-standing partners of the FARE network, we call on UEFA to take action and impose appropriate sanctions."
Television footage shows Mourinho using the word while inspecting the pitch at the Luzhniki stadium on Monday.