I think domestic matches and matches in the Champions League are very different, even though they lost against Real Madrid, Barca still has a chance to perform much better in Champions League because I'm quite sure that Xavi knows how to divide his performance well to be able to work hard. in the champions league to try to appear strong with the players he has and it is proven that in this champions league Barca is able to perform very well to be able to qualify for the next round showing everyone doubts that Barcelona will at least continue to win in every match in this champions league.
Personally I don't think the loss Barcelona suffered against Real Madrid in their domestic league will in any way be a problem to them I'm the champions league because Real Madrid is way better when compared to their next opponent in the UCL Shakhtar Donetsk, with Real Madrid I could consider that loss a fair one even if it was sad they Barcelona was leading before they later lost at home.
Definitely Barcelona will do much better in the UCl regardless of that performance in the la Liga over the weekend, they are in a group where they look like the most superior when compared to everyother team in the same group, over the week, we will be having the fourth round of the UCL where Barcelona will be playing against Shakhtar Donetsk from away but I don't see any advantage on the side of Shakhtar Donetskim this fixture.