The Rossoneri coach is aware of the Catalans' strength, but has insisted that the Serie A champions need to score at San Siro in order to have a chance of progressing
Allegri is well aware that the Serie A champions face two complicated encounters against the holders, but has insisted that they need to score in the first leg in order to have a chance of reaching the semi-finals.
"Against Barcelona, we need to reduce the amount of errors. We have to play offensively, because we need to score to advance," Allegri said during the pre-match press conference.
"We can't play like [Jose] Mourinho's Inter did at Camp Nou. They were a more physical team and we are more technical. This Milan side is not built to defend with everyone near the penalty area.
"It will be two difficult matches, because they are the best team in the world. We have to be ready and play well."
The 44-year-old went on to discuss the absence of Thiago Silva, and insisted that the Rossoneri have what it takes to cope without the Brazil international.
"Thiago Silva is a champion and we will definitely miss him versus Barca. But [Alessandro] Nesta is ready and I have other players at my disposal. I would have liked to face Barca with my strongest team, but that doesn't mean that we are not ready to face them.
"[Kevin-Prince] Boateng and [Zlatan] Ibrahimovic will start. I still have to decide who will be Ibra's partner in the attack. We will evaluate Robinho's condition today. If he doesn't make it, then we have Stephan El Shaarawy and Maxi Lopez ready."
Allegri also took the time to praise Ibrahimovic, and revealed that the Sweden star is very easy to work with.
"It's very easy to be Ibra's coach. He is an exceptional guy, and he gives a lot to the squad and his team-mates."
Wednesday's first leg at San Siro kicks off at 20.45 CET.