However, Allegri has warned his team they must remain cool and play their own game in order to hold off the Catalan giants, who overturned a 4-0 first-leg deficit against Paris Saint-Germain in the last round.
"The most important thing is that we forget the three goals in the first leg and play to win again," Allegri stated at Tuesday's media conference.
"We have huge respect for Barcelona and we know that we will need to play even better again to go through.
"Not a lot will have changed about Barcelona: they will still have the same weaknesses and strengths. We need to keep our heads and find a way to score at least once.
"We need to defend well and attack well. Simple.
"We must not get carried away by the occasion. If we keep our cool and play our own game, we will be OK.
"Juventus have grown gradually as a European power; we need to be at least in the last eight every season."
There were concerns over Paulo Dybala's fitness after the Argentinian suffered a knock in the Serie A win over Pescara at the weekend, but Allegri confirmed the attacker is fit to play.