THEY SAY YOU are what you eat but in the case of football managers it’s more fitting to use an architectural analogy and say you build what you were. Sure, it’s not as catchy but it is more accurate.

So while Jupp Heynckes’ treble-winning Bayern team’s consisted of Bastian Schweinsteiger and Javi Martinez acting as the foundation upon which Munich’s front five could flourish, the keystone of Pep Guardiola’s refurbishment efforts is undoubtedly Philipp Lahm.

There were a few raised eyebrows when the former Barcelona manager decided to convert Lahm from his usual role as a swashbuckling full back into a deep-lying midfielder but when you think that he once described the German as “the most intelligent player” he has every coached, you get a sense that Guardiola sees something in special in the 30-year old.

It doesn’t take a genius to work out what that something special is.

Lahm is, after Sergio Busquets, Pep 3.0 and — just as virtually everything Barcelona did went through Guardiola in his playing days — most of Bayern’s success stems from Lahm linking up with the likes of Franck Ribery and David Alaba.

By way of demonstration, and in case you haven’t seen the tweet, this is how crucial Lahm is to Guardiola’s plans:

(You may have to click the picture to see the full picture.)

What makes Lahm such a scary prospect in this role is his accuracy. According to Squawka, in the Champions League this season Lahm has completed 95% of attempted passes, the joint — with Busquets — best record in the competition.

He also leads the cream of European talent in assists (3) and key passes (13).

Even scarier for United, and on the night they were being dismantled by Manchester City last week, Lahm completed 134 of his 134 attempted passes. The soon to be former Premier League Champions midfield of Michael Carrick, Marouane Fellaini and Tom Cleverley completed just 136 between them.

Lahm is also the perfect player for this keystone role because he has a full back’s ability to switch between defence and attack with consummate ease and, with the laws of physics ensuring a football will always move faster than a footballer, the diminutive German isn’t even open to being out-muscled.

This was proven when United’s next-door neighbours tried — and, for the most part failed — to bully him with Fernandinho and Yaya Toure in the group stages of this year’s competition.

But there is a template to stopping Lahm, even if it is 20 years old and one that Guardiola himself will be all too familiar with.

Most people remember the 1994 European Cup final for Dejan Savićević’s exquisite lob just after half-time as AC Milan went on to rout Johan Cruyff’s Barcelona 4-0.

However, Guardiola will probably remember it as the night Demetrio Albertini and Marcel Desailly put on a man-marking masterclass, stopping the Catalonian from having any impact in a game they went into as clear favourites, thanks in part to the suspensions of Milan captain Franco Baresi and Alessandro Costacurta.

But not only did Milan win, they completely dominated the game and keeping Guardiola quiet played a huge role in that. They didn’t do it by trying to bully him though, they did it by suffocating him — metaphorically of course — instead.

Every time he turned on the ball one of the Milan pair was there to meet him. On the rare occasion he broke free from one, the other was inevitably close enough to shut him down.

It’s asking a hell of a lot of Michael Carrick and possibly even Marouane Fellaini to do a similar job but the simple reality for David Moyes is that he needs them to have the best 180 minutes of their United careers if the English side stand any chance of progressing.

Of course, Bayern have other players who can inflict damage upon United and Arjen Robben and Franck Ribery have both produced individual moments of magic against them in recent years to knock them out of Europe.

Likewise, there are other pointers in United’s favour. No team has kept more than their five clean sheets in the Champions League this year. United have won their last five European games against German teams and have scored in each of their last 14 against German opposition.

Scoring and keeping a clean sheet is imperative tonight if they are to progress over the two legs, but without keeping Lahm in check, things could get out of hand very quickly.

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