Mancini believes Borussia Dortmund are potential Champions League winners, but points to their dramatic improvement in Europe over the last year.
"They are really strong, one of the best teams in Europe now," he said.
"And I think they can have a chance of winning the Champions League.
"Last season they finished with only four points and went out at the group stage, so it shows the improvement a club can make in a year.
"We didn't do enough to stay in the competition. We are disappointed, yes, but we can do nothing at this moment.
"We made mistakes in a lot of our games. It's impossible to win all the time, but we need to understand why we went out, why we made those mistakes, and try to improve next year."