This is a very tricky match, I wouldn't want to be Lucho at the minute. I would think twice about going 3-4-3. I don't think Messi can influence the game as much from the AMC position as Real Madrid always crowd the midfield and ruin his game. Now, if Neymar was here we can simply switch the game to Ney and have the play go through him with Messi getting a few dribbles or touches in and getting that one chance to hit on the break.
But.
Neymar ain't playing, Paco on his best day is Neymar's bad form, a part of me wants to play Alba as LW if we go ahead with the 3-4-3 with a back three of Umtiti and Pique and Masche, I don't trust Paco (who in all fairness is playing his socks off) nor Denis, also, NO GOMES please.