That game is going to be a very interesting match to watch , Barcelona are topping the Spanish league right now, and they are playing very well at the moment, they are always good in possession and they have the most prolific number 9 at the moment which is Robert Lewandowski, while Manchester United at the moment and still developing they are like under dog to Barcelona at the moment but football anything is possible, now that one of their key player is now injured, the likes of Christian Erikson, is going to be another set back for them. But lets watch and see. Like i said before the game is going be a very interesting game to look out for.
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.
In the end we have to look at the actual matches of these two clubs to see who is actually better, Manchester United or Barcelona. Now I see a lot of people who make Barcelona the favourites, it's seen from their position in La Liga and also the wins they got more than Manchester United. But when talking about that, the English League is of course for Manchester United because in the Premier League there are so many tough clubs unlike in La Liga. I don't mean to think that La Liga is an easy competition, but it is true that competition in La Liga is not more competitive than the Premier League, considering the many clubs that can provide tough competition.