Dier has been hit with a four-match ban for storming the stands to confront one fan after the FA Cup tie with Norwich City earlier this season.
Mourinho heralded Dier's personality and potential, and claimed he was the wrong person to be made into an example.
"He's a top level boy," Mourinho said. "He's one of these guys that looks older than he is, the way he thinks, you can see the example that he is at the social level, you can see his profile even socially without being married with kids, he looks really a family stable guy, very easy to communicate with and it's not because he speaks perfect Portuguese.
"It's not because of that that our communication is so, so easy. He's really a young guy with a lot of potential, part of his football qualities, a young guy with a lot of potential. To choose somebody to be the face of this decision, I think is the wrong guy.
"Of course he is [a leader], he is one of the captains. To wear or not to wear the armband in a certain match is not the most important thing. A team needs more than one leader.
"It happens many, many, many, many times that the real leaders in some dressing rooms are not even the captains. I have to say that is a great situation to have the captain of England and the world champion captain in the same dressing room.
"So that's a good starting base. When I keep opening the door for a certain kind of leadership that I want, with time, he'll feel with more confidence and with more freedom, he can exert that leadership."
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