Flick confronted Cuadra Fernandez after Robert Lewandowski's first-half goal was denied for offside
The German demanded an explanation from the ref at the break.
Cuadra Fernandez said, "What can I do? If the VAR tells us it's offside, why would we make it up? For you it's nothing because it's against your team.
"Listen to me... but why are we going to make up an offside?"
Flick said at the end of the 1-0 defeat, "I told him that it was a bad decision to offside Lewandowski. That's all I can say. It was a wrong decision. It's not his fault and I know that . That's all I can say. Nothing more."
Barca goalkeeper Inaki Pena also said: "There was a possible error in marking Robert's foot. Let's hope that if there was such a serious error, LaLiga will act. If it was a mistake, let it be proven, let it be investigated and let them act."