Perhaps there is some encouragement to be drawn for Arsenal from the fact that last time they played Bayern Munich, they won. Perhaps there is some encouragement to be drawn from the thought that, last season, Bayern only beat them on away goals, that no side came as close to eliminating Bayern from the Champions League as they did. But then you think back to the first leg, to Bayern's 3-1 win at the Emirates, and the gulf between the sides becomes obvious. Arsenal have improved since then, but so too have Bayern and, under Pep Guardiola, they are as tactically flexible as any side in Europe.
There would be reassurance if you could examine the two legs last year and isolate something Arsenal got wrong in the first leg that they them put right in the second, but the truth is that Arsenal got back into the game primarily because Bayern were complacent. In the first leg, Arsenal suffered in the way they had against Barcelona in two of the previous three seasons: they came up against a side at least as technically good as them who pressed the ball with far more intensity and focus. The first goal, for instance, stemmed from a move that sprouted from Toni Kroos dispossessing Laurent Koscielny just inside the Arsenal half. Come the second leg, some of that energy and discipline had gone and Arsenal found themselves less harassed on the ball.
Arsenal tried to counter Bayern's press last season at the Emirates by playing Theo Walcott as the central striker, using the threat of his pace to force Bayern to defend deeper. That worked to the extent that there were spells of Arsenal possession, but Bayern's two banks of four were well enough organised that Arsenal rarely looked like breaking through. Walcott, of course, is not an option on Wednesday, and so Arsenal will be forced to do what they did in the second leg and play Olivier Giroud, who at least gives them the option of bypassing the press with more direct play.
Since then, Bayern have lost just once (not including their 4-2 DFL Supercup loss to Borussia Dortmund) and Manchester City's victory in the Allianz Arena does offer some hope, if only in that it showed Bayern under Guardiola are not invincible. That, though, was an odd game at the end of the group stage after both sides had already qualified, and even then City had to come from 2-0 down, had fewer shots on goal and less possession.
It was telling, though, how well James Milner closed down the right-back Philipp Lahm and the effect that had. It's become increasingly common over the past decade for the highest level Champions League ties to hinge on the battle between a full-back and a winger. Usually that's because of the way modern full-backs surge forwards, the clash with the opposing forward becoming sometimes a gauge of who's on top, and sometimes a decisive factor. With Lahm, the dynamic is slightly different: he is not just an attacking full-back, he is also the central intelligence of this Bayern side, the player who sets the tone and the tempo. That's not to say that if you stop Lahm, you stop Bayern – there are plenty of other players capable of shaping a game – but if Lahm can be disrupted then their rhythm becomes just a little less fluid.
The problem for Arsenal then is working out where Lahm will play. Although he operated at full-back against City, in the majority of Champions League fixtures and in the last six Bundesliga games, he has played in central midfield with Rafinha at right-back. If Lahm plays at full-back, that puts a great onus on Santi Cazorla, who will presumably be restored to the left side of Arsenal's 4-2-3-1. Although he is not the most naturally defensive player, he has made an average of 1.5 tackles and 1.1 interceptions per game this season which, combined with his attacking threat, may check Lahm to an extent. If Lahm plays in the middle, the difficulty for Arsenal is even greater; they would naturally play Mesut Özil against him and Özil, quite apart from how weary he has looked recently, is probably Arsenal's weakest player defensively (0.9 tackles and 0.2 interceptions per game).
Although Mario Götze could operate as a false nine, it seems likely Bayern will start with Mario Mandzukic as a central striker. Arsenal should be able to deal with him aerially, but the bigger issue is the space his movement creates. Liverpool last week showed how vulnerable Arsenal can be if opponents are able to run at them, and that means the two holding players have a critical responsibility to protect Per Mertesacker and Koscielny. That is something Mathieu Flamini will relish, but Arsenal will miss the calming presence of Mikel Arteta alongside him.
Behind it all is the fundamental issue of whether Arsenal should try to press and disrupt Bayern early, or whether they should sit back and try to absorb pressure before springing forward on the counter, using the pace of Cazorla and Alex Oxlade-Chamberlain. Given how their pressing has been exposed in recent ties against teams similarly good in possession, Arsenal are probably better off sitting back – as they did at times at home against Southampton and Everton – and hoping they can prevent Bayern passing through them.
If they do that, it's hard to see what purpose Özil serves and there is perhaps then an argument for using Tomas Rosicky and Jack Wilshere in front of Flamini and switching shape to a 4-3-3. Making such a fundamental change of shape for such a key game, though, would be a huge gamble – and the last two sides to have beaten Bayern have both used a 4-2-3-1.