Mijatovic has been a consistent critic of Vini over the past 12 months.
Asked if he would offer the Brazilian a new contract, Mijatovic told Marca: "I don't like to talk about what I would do, because that would influence my friends who work there.
"(Real vice-president) José Ángel Sánchez is a friend of mine, and Florentino Pérez is one of the best presidents in the club's history. From the outside, it's a bit unsightly, it's frowned upon.
"Many people think I have something against Vinicius, quite the opposite. I think he's an excellent footballer, who has always scored goals in important matches, even in Champions League finals, but it must also be said that his behaviour, the way he does some things, isn't good.
"And that needs to be said. Because it doesn't help anyone to tell him, 'Don't worry, it's okay.' Because he's making mistakes. And I think he's a fantastic footballer who needs to calm down a bit, his behaviour, and if he can't do that, then reach an agreement.
"Renewing his contract or not is up to the club, but I believe that Real Madrid can't tolerate any player who isn't happy, and no player who isn't happy at Real Madrid can perform well.
"So it's very simple: either we continue fixing things or we separate and that's fine. Many great footballers have left and Real Madrid has continued winning."