I'll look into that possibility later, but I think Manchester United could be the favorites at Old Trafford. About Manchester United, they are much better now and I'm happy with what they had at Camp Nou yesterday.
In how many league matches, if I'm not mistaken, Barcelona only conceded 7 goals. When against MU, only 1 match, Barcelona has conceded 2 goals. From that match, we can see that Barcelona's defense counter is not a 1-2 bait or a true pass. But just dribbling, Barcelona defenders tend to be solitary and compact, but if your opponent is dribbling, it looks like Barcelona's defense can be penetrated. I also believe in MU's second leg there is a greater chance of winning.