Arsene Wenger will mark his 200th Champions League game tonight, tasked with perhaps the most difficult fixture in European football.Not only do Arsenal have to go to Barcelona and win, he must somehow conjure up a way of overturning a 2-0 deficit and win by three clear goals.As if that wasn't hard enough, his Gunners side are suffering their usual end of season slump, with the Frenchman coming under intense criticism recently.Yet another Premier League title challenge has faded away, while he was denied the chance of making it three FA Cup wins in a row by Watford over the weekend.The tide appears to be turning on the Emirates boss as questions over his ability to instil a winning mentality into his sides intensify with every loss.Laurent Koscielny has returned after a calf problem to aid his unlikely cause, though Petr Cech, Alex Oxlade-Chamberlain and Aaron Ramsey continue to miss out.Danny Welbeck gets the nod up front in place of the much maligned (at this level anyway) Olivier Giroud.For the hosts, Gerard Pique's strategic yellow card in North London rules him out, so Jeremy Mathieu steps in to partner Javier Mascherano in the heart of defence.As ever, the Blaugrana are able to call on the ridiculously talented attacking trident of Lionel Messi, Neymar and Luis Suarez as they look to finish off their visitors this evening.So, here's a closer look at tonight's teams:

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