Mancini's side return to Serie A against Cesena on Sunday after three Juan Pablo Carrizo errors helped the Bundesliga side to victory in the last 16 first leg tie.
Goalkeeper Carrizo was defended by Mancini after the defeat at the Volkswagen Arena, with the Inter boss quick to reiterate his happiness with Inter's recent efforts.
"The formation isn't important; what matters is the character and mindset the players go out there with," he said.
"No one's let me down. When the players cross the white line they give 100 per cent.
"It was a very open match and we lost it because of our own mistakes - they're part and parcel of the game.
"You can't blame Carrizo. Players make mistakes like anyone else. He's an excellent keeper like [Samir] Handanovic."
Inter lie six points off Fiorentina and the final European place, with the Milan derby to come next month.
"Cesena, Sampdoria, two more and then the derby. If we play these games well, we can close the gap," he added.
"We're a bit tired with all the travelling, but I doubt we'll change much [for Sunday]. We'll assess [Gary] Medel and [Rodrigo] Palacio."
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