With both sides already through to the next phase of the Champions League, the battle now is for the top spot in Group H. Barca currently sit at the summit of the table with ten points, two more than their Italian counterparts.
Having already left the hallowed Nou Camp cathedral with a point thanks to their 2-2 draw on match day one, Milan boss Allegri has ordered his troops to maintain their focus against an exhilarating Barca outfit.
"It will be a great challenge, and we'll do our best to win. We have to play a fantastic game, with great intensity and focus, especially in defence - perhaps even more than the previous meeting at Camp Nou," Allegri told uefa.com.
"Every player, the strikers too, will have to help out in defence, to press them when they get the ball."
"The first game against Barcelona was unusual because we scored after a few seconds; we had more chances than them in the first 20 minutes. They had a lot of the ball and this is their most important weapon."
Swedish forward Zlatan Ibrahimović's acquaintance with his former employers from Spain will add extra spice to an already mouth-watering affair but Allegri shrugged off the hype surrounding his mercurial attacker.
"Zlatan Ibrahimović is really quiet and clear," he added.
"He's as motivated as the rest of his team-mates. We need to be very confident, and play with respect but not fear. If we win against Barcelona, we can take a lot of satisfaction and confidence."
Barcelona chief Pep Guardiola meanwhile, has admitted that his side must keep close tabs on Milan's frontline in order to nick a positive result.
"We will have to play a perfect game if we want to win. Milan are a very strong team, great on the counterattack," Guardiola remarked.
"They have Pato, who is very fast, and Ibrahimović at centre-forward is fantastic. Ibrahimović helped us a lot when he was at Barcelona [in 2009/10]."
"He's a formidable player, who has done important things for Italian football and continues to play well. If we meet I'll greet him."
Guardiola also expressed his awe at leading his side out against the seven-time European kings.
"Our aim is to win the match, not to draw. When you play here in Milan you breathe in the air of tradition and history," he purred.
"It's a privilege and an honour to play against a prestigious team like AC Milan. I'm very lucky to be the coach of another great side in Barcelona."
A victory for the Catalan giants will all but see them qualify from the group as winners.
Brazilian hotshot Alexandre Pato is available after recovering from a thigh problem but Antonio Cassano, Gennaro Gattuso, Philippe Mexès, Mathieu Flamini and Clarence Seedorf are all ruled out for Milan.
Barca rightback Daniel Alves is suspended after picking up three yellow cards in four games and he is joined on the sidelines by injury hit victims Andrés Iniesta, Adriano and Ibrahim Afellay.
Milan last tasted victory against Barcelona on 20 October 2004 in the UEFA Champions League group stages when Andriy Shevchenko netted the only goal.