This match will be the most exciting in the Europa League compared to other matches, if Xavi understands better how to maintain a good record against Manchester United, then Erik Ten Hak also wants to set a new record in beating Barcelona, especially when Erik Ten Hak has Casemiro who really understands how playing Barcelona.
That's weak assumption, I guess. Casemiro is no longer at Real Madrid and he shouldn't be relied on to stop Barcelona alone. Under Ten Hag, Casemiro took different form because he was never the same as he was at Real Madrid. So what do you expect from Casemiro?
Ten Hag has the chance to win the match, and so does Xavi. I think it will be interesting, but definitely not El Clasico just because of Casemiro because you can never blame Casemiro himself when he failed to stop Barcelona.
If it is said that Barcelona is able to control the game, then on the other hand I hope that Manchester United will win even though statistically they lose possession of the ball, because football matches are not always won by those who play well statistically.
Control the game and score goals, at least that's the instructions from every coach including Xavi. Playing well is the way to create better chance of winning, even if they are not 100% capable of winning every game. You're only hoping for luck if you only rely on your assumptions.