The pair clashed after Eibar refused to put the ball out for an on-field injury, a policy of coach Jose Luis Mendilibar which is well known.
Casemiro, however, was still upset and confronted Angel during the game.
The defender later said: "I know him from Porto, he seems to me a good uncle but today he is confused.
"It's not for me to tell you what he said to me. He told me I'm an a**hole. I thought it was a bullying attitude, I do not like him or anyone else doing that. I'll always report it.
"You'll never see me face someone if the other does not want to."