|Milan provide reigning champions Barcelona (pictured) with their first major challenge of the season [GALLO/GETTY]
Looking to put a domestic slip-up aside, Barcelona will open the defence of their Champions League title against an AC Milan team missing injured forwards Zlatan Ibrahimovic and Robinho.
Real Sociedad rallied from a two-goal deficit to draw 2-2 with the Spanish champions on Saturday following weeks of speculation that Barcelona would face few challengers aside from Real Madrid as it vies for a fourth straight league title.
While Barcelona has started the season by winning the Spanish and European Super Cups, defensive lapses appear to be its foremost problem but Milan's normally potent attack is short of forwards with Milan coach Massimiliano Allegri ruling Ibrahimovic and Robinho out.
Ibrahimovic's anticipated return to the Camp Nou for the first time since his turbulent exit before last season will have to wait after the Sweden striker injured his hamstring in training. Robinho has yet to recover from a groin injury.
Barcelona defender Carles Puyol should return for the first time since May after recovering from knee surgery, but defender Gerard Pique is out injured, leaving Eric Abidal to likely fill the other center back spot.
"I am calm about tomorrow night, it isn't a final, just the first match of the group stages"
Milan's Massimiliano Allegri
"We have to do better and prepare better," Barcelona coach Pep Guardiola said after the draw, which began with Lionel Messi, Andres Iniesta and David Villa on the bench.
Barcelona and Milan are favoured to advance out of a group that also includes BATE Borisov of Belarus and Czech club Viktoria Plzen, who meet Tuesday in Prague.
Barcelona midfielder Thiago Alcantara said his club's intensity dropped in the second half of Saturday's draw, showing that the team many are comparing with the all-time greats are not invincible.
"I am calm about tomorrow night, it isn't a final, just the first match of the group stages,'' Allegri said on the club's website on Monday.
"We are playing against a side that has won so much but our aim is to get through the group stages."
Stopping Xavi and Iniesta
Alexandre Pato and Antonio Cassano are Allegri's lone options in attack with Ibrahimovic and Robinho out.
Former Barcelona players Mark van Bommel and Gianluca Zambrotta also return to play their former club, with Van Bommel lining up against Xavi Hernandez and Iniesta for the first time since Spain's 1-0 World Cup final victory over the Netherlands last year.
While that final in Johannesburg was remembered for the Dutch team's bruising display, Milan knows Barcelona's midfield must be held in check with Cesc Fabregas and Sergio Busquets also to worry about.
| Barca will be without talented Chilean Alexis Sanchez who is out with a thigh injury [GALLO/GETTY]
"The key players are Xavi and Iniesta - their right brain and their left brain. If you stop them it becomes difficult for their forwards to score,'' Milan midfielder Kevin-Prince Boateng said.
"Teams can't play without their brains."
Barcelona's attack will be without Alexis Sanchez after the Chile forward injured his thigh against Sociedad.
Boateng appears set to play despite bruising his shoulder during Milan's 2-2 draw with Lazio on Friday in their Serie A opener.
Midfielder Gennaro Gattuso is questionable with an eye injury and Clarence Seedorf should also be available after sitting out against Lazio, with Allegri promising changes to his lineup against Barcelona.
Barcelona are unbeaten in their last 10 Champions League games at the Camp Nou.
In 11 prior meetings, including the 2006 semi-final series won by Barcelona, the pair have each won four times and drawn the other three matches.