Girona stunned Barca 2-1, with Fran Beltran scoring an 86th minute winner. Lamine Yamal also missed a penalty for visitors.
Flick said afterwards: “We are not in a good moment, especially in defensive transitions. They have had chances, and so have we.
“Our positioning, especially in midfield, wasn't good. We were too open. We need to calm down. We made a lot of mistakes. We have a long week ahead; I'll give the players two days off so they can reset and improve. There's a long way to go; we're currently in second place.”
A flashpoint was Girona's late winner scored by Beltran. The visitors insist Jules Kounde was fouled in the build-up by Claudio Echeverri.
Flick also stated: "What do you think? A foul, right? No need to say anything more.
"If we had played well, I could criticize the decision. But I don't want to use it as an excuse. We have to focus on our work and improve ourselves. We're not showing our true potential.
"We have to get back to our best, and some players like Pedri and Rashford will be back soon.”