We have seen a lot of favorite teams losing to weaker teams this season, Watford might be one of the few teams stuck at the bottom of the table currently but I think the players of Watford are fighting very hard to try and get their team out from the relegation zone, maybe Watford might still be able to get some points when they play against Manchester United today.
I don't think the result is draw or even Man United lost, United play at Old Trafford and the result won from Chelsea increase their motivation to win again because if they wins, they can go to position 5 with an opportunity to go to UCL next seasons.
I agree with @Strongkored Manchester United will not experience defeat or get a draw, unless Walford gets luck. Surely Manchester United's motivation comes from the previous week's victory. Which is where the United Man can get a win at Chelsea home.
But anything can happen in a match, let's see the match.