I'm very sure that Man United is possible to beat Lyon. Man United performed well in UEL, they have enough players to play against Lyon. It is true that there are some injured players, but I think it won't be a problem for Amorim. Lyon is also not a very big team in Ligue 1, Man United has enough quality players to eliminate Lyon. Even if it will be a tough match, Amorim should have the way to deal with Lyon tactics. For the international match, Amorim looks better during he is managing Man United. So, I'm confident about Man United defeating Lyon.
If it were under different circumstances, I would have agreed with you that Man United would win Lyon without any problems because Lyon, too, is not in a good form currently. They seem to have been better as the season progressed, but they're till not in top form, so if United were in top form, they would have won, but they're not.
We saw how it was difficult for United to win Sociedad, and that is how most of the games they won have been. They struggle to score and defend well. The red card Sociedad got in the second leg was what turned the game around.
If Manchester United want to win the UEL, they have to get better because teams like Atletic Bilbao and Lazio won't make it easy for them. Those are very good teams that can break United's heart.