Allegri acknowledges his team will be underdogs but is taking confidence from their performances against Barca last season, when they faced the Catalans in both the group stages and quarter-finals of the Champions League.
Milan, who last won the European Cup in 2007, held Barca to a draw at the Nou Camp in September 2011 while they also drew the first leg of the last-eight clash before the Spanish league leaders went on to win the tie 3-1.
Allegri told a press conference: "Milan-Barcelona means we are facing the best team in the world but I do not accept that in the last two weeks everyone has been making us out to be the sacrificial lamb.
"As long as the rules do not change then we start the match tomorrow [Wednesday] evening in the same position, 0-0.
"In the last two years we have played well against Barcelona, we played well in the quarter-final last year.
"We know that at the moment they are the best team in the world but we have to try and create the elements to go through to the next round, although we know that whoever they play against they have an average of 65% possession.
"We have to try and limit their possession, making them less dangerous because they are so dangerous when they go forward. We have to be good at managing our own possession because maybe they will concede something at the back.
"We have to step onto the pitch with the conviction that we can go through to the next round. I know we will do well, then if we are a little lucky we can hope of making the quarter-finals."
Allegri has been boosted by the return to fitness of striker Stephan El Shaarawy, although Mario Balotelli is not eligible having played for Manchester City in the competition this season.
Meanwhile, Barca playmaker Xavi is also available but neither David Villa (kidney stones) nor Adriano (hamstring) have travelled. Youngster Oier Olazabal has been included in the squad.
Barca have been crowned European champions three times in the last seven seasons and are perennial favourites, but forward Pedro was cautious ahead of the clashes with Milan.
He said on www.fabarcelona.com: "We're very eager to get back to playing in this competition against a difficult rival like AC Milan.
"This round has always been difficult for us each year, perhaps because there's such a big break in between matches.
"Milan have always been a difficult side because they have a lot of history and they have very dangerous players. Anything can happen in a two-leg tie in the Champions League. We have to concentrate and be very vigilant in defence."