The Champions League has returned this week and for Arsenal it represents one of the toughest tests of the season. They have the unenviable task of travelling Bundesliga leaders Bayern Munich on Wednesday night hoping to pick up a result to take back to the Emirates Stadium.

It's a tough ask and not really the reward the Gunners were looking for after winning their group so superbly last year.

It's not all doom and gloom for Wenger's men, though, this Bayern side aren't as imperious as they've been in recent years with Carlo Ancelotti not exactly winning over supporters after the exit of Pep Guardiola last summer.

There are ways Arsenal can get at the Germans and if they can pick up a draw or even an incredible win then they'll be in great shape for the second leg.

Here are the THREE Bayern weaknesses that the Gunners should exploit...

Smash the left flank

Philipp Lahm announcing his retirement at the end of the season has sent shockwaves around Germany over the last week. It was a controversial move with the Bayern hierarchy somewhat unhappy with his decision to announce it in such a fashion.

As quoted by The Sun, chief executive Karl-Heinz Rummenigge said:

"Bayern Munich are surprised by the actions of Philipp Lahm and his advisor."

Hardly the ideal situation heading into the knockout stages of UEFA's biggest club competition.

Lahm played at right-back on the weekend away to Ingolstadt but didn't have the best game in a 2-0 Bayern win, before being substituted in the second half. If Arsenal can capitalise on this friction then it could be a way for them to expose what is a very talented backline.

That's not to say Lahm isn't still one of the best right-backs in the world, he is an extraordinary player. Arsenal have plenty of talent on that left-hand side though with the likes of Alex Iwobi and Alexis Sanchez able to put in match-winning performances. If they can overload on that side and give Lahm a battle, the Gunners may be able to show why he's decided to hang up his boots at the end of the campaign.

Bayern's pressure to win big

Bayern's away record in Europe isn't the best - in fact, they've failed to win away from home in their last eight knockout ties in the Champions League. Also losing twice away from home in this season's competition to FC Rostov and Atletico Madrid, it's clear that Ancelotti will be looking for a convincing win on Wednesday night to avoid any potential slip-up at the Emirates.

That puts pressure on the home side and leaves Wenger with a dilemma. Match them toe-to-toe in an open attacking game? Or have his side bide their time to pick off Bayern on the counter-attack?

Given the German side's need to win it could be the latter that proves most effective. We know Arsenal can counter with pace with the likes of Alex Oxlade-Chamberlain and Theo Walcott likely to be in the side, while we know Arsenal can take chances with the likes of Alexis Sanchez leading the attack. Can Wenger exploit Ancelotti's desire to win by two clear goals?

A midfield casualty

As reported by The Daily Mail, Xabi Alonso is facing a fitness battle ahead of Arsenal's visit after hobbling out of a training session with a knee injury this week.

That's a massive boost for Arsenal. Even if he makes the game, it gives the Gunners midfield an edge to exploit, knowing that the Spaniard likely isn't at 100%. If he misses it? Well, Arsenal's stars can impose themselves on the game knowing that Ancelotti has had to veer from his gameplan.

With Granit Xhaka again available, Wenger has a bit of midfield steel of his own to call upon and that could be vital with Bayern looking to exploit the space between Arsenal's somewhat lightweight midfield and their defence. Xhaka, of course, knows all about Bayern having arrived at the Emirates from a four-year stint at Borussia Monchengladbach.

Can Arsenal exploit this pre-match turmoil in the heart of Bayern's midfield?