Back-to-back defeats against Napoli and Juventus have seen Fiorentina bow out of the Coppa Italia while losing momentum in their bid for a European qualification spot.
The Europa League is the club's only chance of silverware this term and Montella urged his players to bounce back in the first leg of their quarter-final.
"The causes are there, we have identified and we have worked to solve our problems," Montella said on Wednesday.
"For days in Florence we have talked about nothing else, we will continue to work on these problems.
"Our problems are not physical, something has happened in all of our heads. We understand where we went wrong and the game with Dynamo Kiev comes at the right time.
"We need to show maximum concentration to overcome adversity."
Striker Mario Gomez has come in for criticism of late, but Montella said all his squad needed to play their part.
"It is wrong to focus on a single player, I expect more from everyone, especially from the more senior players," he added.
"At this point, the Europa League is important to us, and we will play to the end. The league is still open in my opinion, anything could happen."
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