That makes sense, but MANU would be well served by having someone who can hold play in the MF. I am no fan of Mata's game, but I think he would be a useful piece at some point today. I think you are correct and have to go after Barca with speed, so bringing Lukaku on later is a better plan. Looking at United's squad, it's just astounding that Sanchez is so MIA. A threatening winger allowing Rashford to push inside would create a lot of problems for Barca, especially in behind Alba.I know I'm not going out on a limb but I'd expect both home teams to just overpower the opposition.
For United, Luke Shaw and Ander Herrera out hurts. I'll predict the lineup as DDG-Young-Smalling-Lindelof-Dalot-Mctominay-Fred-Pogba-Lingard-Rashford-Martial