Simeone was angered Grado's decision to send off Clement Lenglet on 40 minutes.
Lenglet was sent off after twice being booked for two fouls on Celta striker Ferran Jutgla.
Cameras picked up Simeone's reaction, stating: "You're a cheeky b*****d, you're a cheeky b*****d."
And he said the same thing to the fourth official: "If he's blowing that whistle, he's a cheeky b*****d. He's a cheeky b*****d."
Later, Cholo did not want to enter into further controversy in his press conference and, when questioned about Lenglet's dismissal, he commented: "No, I'm not going to comment on anything. The famous criteria."
Atletico captain Koke also said: "If he decided it, it's a red card. It didn't seem like he had done much either. He could have shown the opponent another card, but he didn't. But this is football. It's better not to comment on the referee."