Christian Erikson's injury is a big blow to Manchester United, even as Barcelona are without Dembele too, but it won't really change the outcome of the match if two of them don't make it to the match squad for that day, Manchester United have players capable of replacing Christian Erikson and Barcelona have players to replace Dembele and that game Wil come down to the mangers tactics, it will be a tactical battle between the two teams and the best thing will come out victorious.
Any team that wins the first leg Wil take that advantage into the second leg and progress, so I think the first leg will be the decided of the tie .