Injuries to Lorenzo Insigne, Federico Chiesa and Alessandro Florenzi have diminished Mancini's options in the forward positions, meaning Juve's Kean – who has only one substitute appearance for his country to his name – is in line for a full senior debut.
But Mancini has no concerns over the 19-year-old's ability to step up.
"We had some doubts on the line-up, but they have now been resolved," Mancini told a news conference.
"We are convinced those who step on to the field will do well, even though others had been playing together for longer and knew each other better.
"We'll see who plays. I expect Kean to do what he does best. He doesn't have Insigne's experience, but does bring physicality, enthusiasm and an eye for goal. We hope he'll bring joy to the team.
"The process of finding a formation to rely on was rushed more than anticipated, but our real objective begins from tomorrow, which is to play good football and score more goals."
Mancini, though, insisted that the qualification campaign for Euro 2020 has always been Italy's prime focus.
"Euro 2020 qualification was the primary objective and we honoured the Nations League to the end," Mancini added.
"But now it becomes fundamental not only that we win, but also improve our ranking and potential draw going forward.
"We'd like to improve our ranking, as the current picture isn't one we like very much.
"I believed in this project from the first day, in the players who were already here and the youngsters who could join us.
"Clearly, there will have to be choices, and the most difficult thing is leaving someone at home. We have improved a great deal over the last 10 months and that is positive."
Liechtenstein are Italy's next opponents, before they take on Greece and Bosnia-Herzegovina in June.