The rivelry between Manchester United and Chelsea is too much that even if one side is on a multiple games losing streak, once they meet, that side on losing streak will pick form. The only advantage that Chelsea will get in this match is that Manchester United is having a final cup coming up very quick, this might make Amorim to rest his players. But if he doesn't rest players, Chelsea can't win Manchester United. I will only place my bet on this match, after the match day squad has been released. But due to the rivelry between this two teams, Chelsea should not expect any favour from Manchester United as Liverpool did them two weeks ago.
I agree with you that this two clubs don't walk on same path as their rivalry has been a long standing one, but saying that Manchester United wouldn't favour Chelsea is this game is tantamount to underrating Chelsea as though they don't stand any chance in getting all 3 points in this match. I hope if Chelsea gets to win this match the excuse from Manchester United fans wouldn't be that it's because they have a europa finals to play that's why they had to not put in so much effort in the game against Chelsea.
This is a fight between two elephants and definitely both Chelsea and Manchester United are in a desperate position to win this match, and for Manchester United losing this match means relegation for them and draw is a bit not welcome, and similar goes with Chelsea, and emotions aside, we can't definitely predict which club will win the match, so betting in a draw dimension is the most profitable odds at this point.
Wether or not Manchester United draw or lose this game to Chelsea they still won't be getting relegated as the three teams Southampton, Ipswich Town and Leicester city has already been certified as the relegation teams this season. But, what I believe Manchester United would be fighting for in this game is for the pride of Manchester against the west London side. It has mainly being a part of the rivalry aside fighting for points. Perhaps, a draw is likely but outside that am giving it to Chelsea if there happens to be a winner because they're the one fighting for a higher course.