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 .
In general, these two teams need to work hard in the first leg to get better and that doesn't mean you have to be more relaxed in the second leg because in the second leg you also need to be more focused so that the good results become clearer. Whatever happens in the first leg, the decision is still made on the results of the matches in the second leg, even though when the results of the matches in the first leg are already available, some people can make predictions more simply for these two teams in the European League.