Manchester United's current attack line is indeed very bad in its finishing. This is also one of the factors that makes it very difficult for Manchester United to win every match. Because basically Manchester United's midfield is quite good at the moment, so the flow of the attack is quite good.
Manchester United attack is so weak, and their defense is weak also. I notice that Manchester United are always creating chances in their matches, but the issues which they are facing is that, they lack players which can convert those chances into goal. If you can check Manchester United last premier league matches, which was against Nottingham forest, Manchester United created lots of chances in the match, if United are having a proper attacker, then they will have conveniently won the match, but they missed all the chances created, and they lost the match.
Manchester United will be playing against lyon, the match won’t be a easy one for the two teams, but if Amorim work on Manchester United, then they should be able to win the match, but the worst mistake which Manchester United will make is allowing Lyon score first in the match, if they can score first, then Manchester United might find it difficult to equalize.