The last time Arsenal stepped onto the grounds at Camp Nou, they were terrorized by one player: Lionel Messi.

Arguably the best player in the world, Messi scored four goals, including three in the first half, sending the Gunners home in the quarter-finals.

Barcelona have the best offense in the world, so slowing down Messi may not mean much since David Villa, and Pedro are both world-class forwards, as well.

But after not scoring when the two clubs played at Emirates Stadium in the first leg, on top of the fact that he was so successful last year against Arsenal, it's safe to assume that Messi will be in his best form and have his eye on the finding the back of the net.

This time, Arsene Wenger will not have Mikael Silvestre and Thomas Vermaelen to mark Messi, as well as Manuel Almunia in the goal.

Now the goalkeeping duties rest on young Wojciech Szczesny. An exception performance today may mean he deserves more consideration for the permanent starting job once Lukasz Fabianski returns from injury

Wenger will likely use a lineup of 4-2-3-1. The central defense is likely to be vital in preventing Messi from executing his trademark runs and deft shots from distance.

Emerging defender Johan Djourou, who suffered a major knee injury in September 2009, will likely be the starter, and may have the chance of his career to prove his skills. The Swiss center back will be responsible for marking Villa and Messi, while his fellow central defender Laurent Koscielny will be responsible for marking Pedro and Messi.

This is certainly not an easy task, especially since Barcelona's forwards are so efficient at Camp Nou.

In the first leg, Wenger pulled Alex Song for Andrei Arshavin for offense with Arsenal down a goal, but Song's absence today means that Abou Diaby will likely take the role of the defensive midfielder. That means Diaby must prevent Andres Iniesta from finding Messi.

Diaby, who has been known for his erratic play, may get some much needed help from Jack Wilshere, who has been praised recently. Containing Iniesta, in a way, may be a strategy to contain Messi.

The Argentine striker is so dangerous that he can score from almost anywhere, but he seems to thrive near the semicircle. Preventing Messi from receiving the ball in that area is vital since he is capable of creating his own shot better than anyone.

Should Wenger get an excellent effort from Szczesny, Djourou, Koscielny, and Diaby, the Gunners may find themselves into the quarter-finals. Wenger knows that's a tall order.

He says a clean sheet is most likely unattainable, but has faith in his defense.