In the best case scenario, they may even manage to stay in 6th place, if Man United continues to play very irregular games.
It's difficult with the rest of their games, I think Tottenham are more favourites than West Ham. But a Man United bug is very likely to happen. But if you look at West Ham's fixture schedule they have a more congested schedule because they still appear in the Europa League. Whereas in the EPL their chances are also tough because they have the rest of the game with a great team, similar to Man United but they have fewer schedules.
Tottenham's initial encounter with Man United ended in a 3-1 game, a small margin of victory, and if it weren't for the fact that they already play at home, Tottenham may beat Man United the next time they meet.
Tottenham isn't left out either, they have a full month of EPL fixtures scheduled, all of which are against top clubs. I wouldn't say they have a little chance, but they do need a lot of energy to burn these men out, or else Man United will have to replace them.