I dont think that Manchester United is an underdog in this match, although I see that Barcelona are the favorites for the first game at the Camp Nou, but this does not mean that they can easily defeat Manchester United. In the second match, things could be even more difficult for Barcelona as Manchester United have a great winning streak at Old Trafford. It is strange to see a match of this level at the stage in the 1/16 finals.
It's not good at all to underestimate Manchester United in the first leg against Barcelona at Camp Nou. I don't agree with this because basically manchester united has proven what he is capable of since the world cup ended. Manchester United's performance is getting better and that's sign that Barcelona shouldn't underestimate him. I also don't expect Xavi to underestimate him, but Xavi and his team need to have good confidence and strong mentality to go against Manchester United.
Barcelona will travel to Real Betis tomorrow for La Liga match, while Manchester United will host Crystal Palace at home. And before the second match begins on February 17, there are still several matches to be completed.