Barella struck in victory over Europa League opponents Bayer Leverkusen for Monday's quarterfinal win.
“Nicolò has always shown his great personality," Rastelli told Radio Music Television.
“When you stand out at that age, it means you have great technical qualities and a great character.
“In the end, that makes the difference. I had not the slightest doubt that Nicolò would carve out a space in the team."