Bellingham was sent off in Real Madrid's draw at Osasuna on Saturday for abusive language towards the referee.
Ahead of Barca's clash with Rayo Vallecano, Flick commented: "I know everything that's happening, they came early and I've been well informed. For me, what's important is to focus on ourselves. It's the best we can do.
"I know it's important for Real to be the leader. For everyone. It's important and it gives confidence. But we have to play and win, and show that we're performing great."
On Bellingham, he continued: "I think it's disrespectful, that's how it is for me. I shouldn't decide and it's not my business. It's not a situation that affects me. But I tell my players not to waste time or energy saying certain things.
"Why talk about this? There's one person who talks to the referee: and it's the captain. I also like handball, he blows the whistle and the ball goes to the ground and you have to defend.
"I don't like this kind of behaviour, and I told my players that today. It's not good for the team. A red card weakens us and we don't want that."