Champions League preview: Messi, Barcelona in danger against Milan

Lionel Messi and Barcelona haven't been eliminated this early in the Champions League since 2007.

Alfredo Falcone/Icon SMI

This week's Champions League games see three of four ties very much in the balance with the prospect of one-time competition favorite Barcelona facing elimination at the hands of AC Milan. It could also be a very quick Champions League return for Wesley Sneijder and Didier Drogba if their Galatasaray team fails against a resurgent Schalke. Bayern Munich welcomes Arsenal with a 3-1 first-leg lead while Porto heads to Malaga with a 1-0 lead. Here's the rundown:

AC Milan at Barcelona, Tuesday, 3:45 p.m. ET

First Leg: 2-0 Milan

Carles Puyol looked like a man possessed Saturday night, and after a much-changed Barcelona side beat struggling Deportivo La Coruna 2-0, the captain clenched his fists and punched the air in delight. Why so happy? Yes, Barcelona continues its inevitable path to a La Liga title. Once again, Lionel Messi, a late substitute, scored for the 17th straight league match, but this was a defensive success more than anything else. Specifically it was the first game in 14 that Barcelona kept a clean sheet. In that time, the Catalan side lost twice to Real Madrid, and dropped the first leg of this tie 2-0 in Milan. Most significantly, it has looked human: sometimes tired, other times tetchy, other times out of ideas -- none of which we have seen in this Barcelona side since the arrival of Pep Guardiola in 2008.

So what is the dip attributed to? Have they been found out? Is Messi human after all (scoring 17 games in a row, what do you think?)? Was it too complacent before the Milan game? Last week seemed to be the first time the club admitted it is now suffering the loss of coach Tito Vilanova, currently receiving cancer treatment in New York.

"The experts say that 30 days into the absence of a leader, there is a decline in performance," club president Sandro Rosell reportedly said.

Gerard Pique made the same analogy.

"We miss him a lot," the defender said. "It's not easy being without a trainer; it's like a company without a director."

The fact he has been seriously ill -- "he is not," Javier Mascherano put it, "in New York on holiday" -- has somehow contributed to his absence not being connected to the defeats.

Certainly Rosell is attaching no blame to his deputy, Jordi Roura, whom he has called "a hero." If Barcelona is eliminated this week, it would be another example of matters beyond the pitch affecting its chances: back in 2010, Barcelona's preparations for the semifinal against Inter Milan were disrupted as the team traveled by bus to Milan following the ash-cloud from Icelandic's Eyjafjallajökull volcano eruption.

So while all eyes Tuesday will wonder if this is the end of an era at Barcelona, it also does a disservice to Milan, which played the perfect tactical game on a lumpen San Siro pitch three weeks ago. OK, so this Italian side is a long (a very long) way from the Arrigo Sacchi's two-time European Cup-winning side of 1989 and 1990, or even Carlo Ancelotti's team in the mid-2000s, which reached three finals in four years.

But it is dangerous, and in Kevin-Prince Boateng and Stephan El-Shaarawy, has two players who raised their game in the first leg. Center forward Giampaolo Pazzini was also excellent, but he is out injured: his replacement, whether it's M'baye Niang or Robinho, will have a tough job holding up the play on the rare occasions Milan has the ball. If the Italians score, Barcelona would need four goals to progress: given its recent defensive issues, Milan has a great chance of completing the upset.

Tip to progress: Milan

Galatasaray at Schalke, Tuesday, 3:45

First Leg: 1-1

Schalke has a lot to thank Galatasaray for: when the teams last met, the German side was on a terrible run of form, one win in 11 games, and coach Jens Keller looked out of his depth. After an impressive 1-1 draw in Istanbul -- if anything, the German side deserved more from the first leg -- Schalke has won three in a row in the Bundesliga, including an impressive 2-1 win against rivals Borussia Dortmund over the weekend. That came at a price, though: Klaas-Jan Huntelaar injured his knee ligament and will miss the game. American Jermaine Jones is also suspended.

Galatasaray is under some pressure now: it underperformed in the first leg, and after Wesley Sneijder was hauled off at halftime, suggestions that there is tension between him and coach Fatih Terim have not gone away. The Didier Drogba-Burak Yilmaz partnership up front looks good, but Drogba pulled rank Friday to take a penalty he had earned against Genclerbirligi, only to drag it wide in a rare defeat for the Turkish champion. Schalke now has the momentum and is the slight favorite to reach the last eight.

Tip to progress: Schalke

Arsenal at Bayern Munich, Wednesday, 3:45

First Leg: 3-1 Bayern

Bayern is 20 points clear at the top of the Bundesliga and has won eight straight league games since the winter break. Is there any glimmer of hope for Arsenal? Not really. Bayern's new forward, Mario Mandzukic, who has scored 19 goals this season, warned teammates not to concede an early goal but admitted that missing out on the Champions League last season has made the team extra hungry this time around.

"Bayern haven't won trophies in two years, and that's unnatural for this fantastic club, so everyone is hugely motivated to make up for what they had missed," Mandzukic told Sportske Novosti. "That's why we're looking so powerful. We're doing very well in each competition, so of course the thought of winning everything is on our minds. We have good depth in our squad, we've been excellently managed and now we only need a small dose of luck."

Arsenal will need more than a small dose to get past Bayern in Munich.

Tip to progress: Bayern Munich

FC Porto at Malaga, Wednesday, 3:45

First Leg: 1-0 Porto

Porto lost its Portuguese league lead last week after a goalless draw with Sporting Lisbon. It bounced back with a 2-0 win over Estoril on Friday but remains second after Benfica hammered Gil Vicente 5-0. The turnaround in league fortunes came at a bad time for coach Vitor Pereira, who must decide whether Porto should stick and play for the draw in Malaga or go for an away goal that should kill off the tie.

Joao Moutinho, the match-winner in Oporto, has been struggling with an injury while winger James Rodriguez made his first appearance in two months last weekend. Both will need to be at their best to stop a Malaga side that beat AC Milan and Zenit St. Petersburg at home in the group stages. If Porto can repeat the high tempo it showed three weeks ago, playing at a pace that gave its opponent no time to settle on the ball, and reduce the opportunities for danger-man Isco, it should be enough to progress.

Tip to progress: Porto