Man United chances of getting full points in the next two matches are actually quite high, because the opponents they will face are not dominant teams. However, Amorim and his team should not be careless and underestimate them, because Ranger and FCSB also have the ambition to finish in the top 8 of the standings in order to automatically qualify for the last 16. Regardless of Man United performance in the Premier League, I think Amorim squad deserves to be called a trophy challenger in the Europa League this season.
So it's true as you said what happened to Man United in the EPL league will not necessarily have an impact on the European league. In addition, I think Amorim is aware that the EPL league will be difficult to catch up to finish in the top four, although the season is still very long but it will be difficult and Amorim is aware of that. So the shortcut is they have to be able to win the Europa League title in order to play in the Champions League next season, it would be more realistic for Man United to focus on the Europa League right now. Moreover, their opponents in the next match in terms of quality, Man United are better than Rangers. so Man United's chances of automatically qualifying for the last 16 are very big.
I am sure Man United will rise, and can be a challenger in the Europa League trophy this season with the squad they currently have. What Amorim needs to do is continue to improve the team, work hard, then in the future Man United will be better.