Robinho saw his opener cancelled out by Murcia midfielder Enrique De Lucas before Guti was dismissed for lashing out at Cesar Arzo.
Mijatovic said afterwards: "Guti cannot react like that any longer, not at such crucial moments in a game. But it's something that normally happens.
"We did well enough in the first-half, but couldn't maintain the pace in the second. I believe fatigue was a factor after international week."
Real coach Bernd Schuster also said: "It is not a special subject. Guti has behaved very well until now. He never has been in danger of getting sent-off. His attitude today has surprised me a lot, but what are you going to do?
"We are not going to overstate this. After the second or third time it happens, we will have to think about it, but this is the first time."