When asked about De Bruyne's absence, Mourinho reacted with a dig at the media's questions before revealing that he was unhappy with the Belgian's performance against Swindon Town and in training.
"This is fantastic because nobody asks me about Mata. You are for three weeks speaking about Mata, and now you are speaking about Kevin de Bruyne. So you are not interested in the players that are playing? You are interested in the players that are not playing," Mourinho told reporters.
"He was not selected. It was my decision. Only 11 can play and 18 can be selected. I try to decide by what they do on the pitch when they play and what they do in training. I try to be honest with Juan and say that he's going to play tomorrow, because of what he did in training and because of what he did in the matches he played.
"With Kevin it's the same. He's not selected because I didn't like the match he played against Swindon and I didn't like the way he was training. But you have this tendency to only ask about the guys that are not selected."
Mourinho's side lost their opening Champions League match against Basel a fortnight ago.