Dear Sir Alex,
I ended up writing this message to you in my blog since there is no way for me to send an email even on the official MU website.
My idea is very simple. But before that I must admit that I am not a professional football coach. I was a player myself, long time ago.
Heard that you are seeking tips from Jose M on how to beat Barca. I think he has a pretty good idea, and that he had put in play. Yet, what he is lacking is a strong, aggressive front line. He had his players crowd the mid area and he had been successful. But since he does not have a very strong front line, he could not destroy Barca. He could only contain them.
So this is my idea. 'Kill" or lock up the key players. Messi is Barca. He sets up, creates chances and even scores goals. Have one person marking him. What Diarra did was correct, but not effective enough. He did not lock the guy up. He lets Messi to move and create spaces to receive the ball. We do not want him to receive the ball. Do this for the first 30 minutes of the game. The remaining 15 minutes, attack. The strength of Man U's counter attack can break both Barca defences. As for Mascerano. Play a little psychology on the guy. Get him heated up, he will be down and cannot play. Chances are this guy will win himself a card.
Please remember, the player designated to locking up Messi does not play much. His only duty is to stick to this guy's body, literally touching, glued to his body in both attacking and defending modes. You need someone with speed to do this since Messi is very slick. He splits away and receives passes.
While you are doing that, please also ensure that Xavi is marked as well. Not to the extend Messi is being marked but just make sure that this guy is not able to make dangerous passes. If you intend to cripple Barca entirely. Lock this guy up as well. Without both of them playing to their fullest, Barca is crippled.
Have your players attacking only in the last 15 minutes of each half. If a goal is obtained, maintain the same 'lock up' strategy. Do not go on entirely defensive mode. Players will tend to make mistakes.
To win, tell your players that no chance is to be missed. No smiling if any one of them misses a chance. This is the most important thing you must remind them.
BTW, there are some great 'divers' in Barca. The whole world knows that but UEFA is keeping an eye closed. One of them is Messi. So the lock up system if it is done correct does not require a tackle. That means chances of this guy faking a foul is minimum.
It will be a good psycho war on papers if you could say something like you are not afraid of Barca and their magic football but the fake-foulers worry you most.
Good luck Sir Alex. I will join you during the match, on TV.