The Rossoneri coach wants his side to believe in themselves when they face the "best team in the world", while he also has been listening to president Silvio Berlusconi's advice
The two European powerhouses come face-to-face on Wednesday at San Siro, and coach Allegri wants his side to play to the best of their abilities and believe they can knock the Liga leaders out of the competition.
"It will be a wonderful night tomorrow [Wednesday], where the most successful club will face the best team in the world. We will give our all and face Barca with courage, strength and spirit, " he told reporters.
"It doesn't matter if we're facing Barca, Juve [Juventus] or Real Madrid. We need to be focused, run a lot and be good technically. We must try to limit Barca's ball possession, and be good when we have the ball as they could give away space.
"We have to step onto the pitch tomorrow with the knowledge and awareness that we can knock them out of the Champions League."
The 45-year-old also said he had spoken to the club's president Silvio Berlusconi regarding the match, and vowed to use the former Italian prime minister's advice to attempt to record a positive result.
He added: "I have spoken with Berlusconi about tomorrow's match. The president always expresses his thoughts and ideas.
"They're often genius and I listen to them, and then I try to field the best possible formation in order to win."
The former Cagliari trainer chose the press conference to reveal part of his side to face the Catalan giants, with Allegri confirming that Cristian Zapata and Philippe Mexes will be paired at the heart of defence, while Riccardo Montolivo will start in midfield.
The coach was less forthcoming, though, in regards to the fitness of striker Stephan El Shaarawy, but he did confirm the 20-year-old would start if he was fit.
He continued: "Our central defence against Barca will consist of Zapata and Mexes. [Kevin] Constant will be on the left, and [Ignazio] Abate on the right.
"Montolivo will play from the start versus Barca. I still have to decide who the two other midfielders will be.
"El Shaarawy will play from the start versus Barca, if he's ready. Today [Tuesday], I will evaluate what is the best formation to face Barca."