Arsenal face a daunting task but how could they beat Barcelona?

The odds are stacked against Arsenal as they look to overturn a 2-0 deficit in the second leg of their Champions League last-16 tie against Barcelona at the Nou Camp on Wednesday.

The Gunners were left with a mountain to climb after succumbing to a late double from Lionel Messi at the Emirates three weeks ago, as Barcelona punished two costly lapses of concentration to leave north London with a commanding lead.

In order to stand any chance of keeping their Champions League dream alive in Spain, Arsene Wenger's side will need to win by two goals. Their recent struggles do not inspire confidence, and Barcelona's brilliant form highlights the scale of the task ahead.

While Arsenal have won just four of their last 14 games, Messi, Neymar, Luis Suarez and Co are unbeaten in 37, and Barcelona haven't lost a home game by two goals or more since a 3-0 defeat by Bayern Munich in May 2013.

It all adds up to a near-impossible task for Arsenal - but how can they go about pulling off a miracle? We take a look at some of the ways in which they can give themselves a chance…

Stop Busquets

It was Messi who took the headlines at the Emirates but Barcelona's orchestrator Sergio Busquets was equally important. The midfielder is often overshadowed by his superstar team-mates, but Luis Enrique describes him as "fundamental", and the Gunners were punished for failing to nullify him in the first leg.

Busquets provided the platform for Barcelona's victory, completing more passes and creating more chances than anyone else on the pitch. At the Nou Camp, Arsenal must put him under greater pressure in order to cut off the service to the front three and force the hosts to adopt a more direct approach.

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The tactic has worked well against Barcelona this season, particularly in Celta Vigo's 4-1 victory against them in September. Busquets was overwhelmed by the feverish pressing, with his pass accuracy dropping from his average of 90 per cent to 80.5 per cent.

His mistakes were punished that day, and Barcelona struggled to find their usual fluency in possession. The video above shows how Celta did it, and Wenger would do well to take note - especially after the role the Spaniard played in the first leg.

Press Barcelona's defence

Arsenal were able to limit Barcelona's threat by sitting deep and soaking up pressure for around 70 minutes of the first leg, but a more proactive approach might be necessary at the Nou Camp.

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As well as pressurising Busquets in midfield, Wenger will need his forwards to chase down Barcelona's back four in an attempt to force mistakes high up the pitch. It's a risky strategy and one that could see them tire later in the game, but it could also be key to their hopes of scoring the goals they need.

Alexis Sanchez certainly has the work-rate to contribute, and Wenger might also be better off giving Danny Welbeck the nod ahead of Olivier Giroud. The England international has impressed since his return from injury, and he offers far greater speed and mobility than Giroud. On the right flank, Arsenal will need the same kind of industry from either Joel Campbell or Theo Walcott.

Take their chances

Arsenal's dismal finishing has been a theme of their season, but capitalising on the scoring chances that come their way at the Nou Camp will be absolutely imperative.

Barcelona will dominate possession as they did in the first leg, but there will also be opportunities for Arsenal to counter-attack as they did at the Emirates, where they wasted a string of openings before Messi's late salvo.

Alex Oxlade-Chamberlain missed what Wenger described as an "unbelievable" chance midway through the first half that day, while Aaron Ramsey and Giroud were also guilty of squandering opportunities. With a minimum of two goals required on Wednesday, they simply can't afford any more of the same.

Keep their discipline

The temptation for Arsenal will be to charge out of the blocks and throw everything at Barcelona, but the first leg showed the importance of keeping their discipline. Messi's opening goal at the Emirates was a result of the Gunners over-committing and leaving themselves vulnerable to the counter-attack, and they'll need to be more savvy on Wednesday.

Koscielny boost for Arsenal

Arsenal defender Laurent Koscielny is fit to face Barcelona in Wednesday's Champions League clash.

Barcelona are, after all, the most devastating team around on the break, so Arsenal will need central midfield duo Francis Coquelin and Mohamed Elneny to ensure there is not too much space to exploit in the event that the Gunners are robbed of possession in Barcelona's half.

Judging by his comments after the first leg, this will be an area of close attention for Wenger. "They are better than us and everybody knows that," he said, "but I believe we could have won the game tonight if we had kept the discipline until the end."

Pray Barcelona have an off day

The reality, of course, is that even a Herculean effort might not be enough for Arsenal to overturn the two-goal deficit against arguably the greatest club side in the history of the game.

So as well as producing the performance of their lives, Wenger's players will need to pray Barcelona fall short of their usual standards...

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