A win for the Red Devils would close the gap on Manchester City to five points ahead of the leaders’ own match against Southampton on Wednesday.
But the Hornets have won their last two games without conceding, and Man United coach Jose Mourinho looked ahead to the match with praise for his rivals.
“I think they have a squad full of very good players, which is not normal for these mid-table teams,” Mourinho told reporters. “They have a good coach, and they have improved a lot since the last season, too.”
Arsenal looking to pick up points
Boosted to fourth position after a 1-0 win at Burnley on Sunday, Arsenal are looking to build on momentum for a shot at the title.
While trailing Man City by 12 points, they have a chance to pick up points when they host Huddersfield Town on Wednesday.
“We have a good chance tomorrow to take three points at home and that is the only thing that matters,” said Arsenal manager Arsène Wenger.
The manager also ruled out selling Mesut Ozil and Alexis Sanchez, both of whom are out of contract in the summer and have been the subjects of speculation of impending departures, possibly for Man United and Man City, respectively.
“As long as they are here they have to give their best for the team and for the club,” Wenger said. “Unless something unbelievable happens, I don't see why it should change.
“They are going into the final year of their contract and will they stay longer? That's impossible to answer today, because I don't know, but they have a contract until the end of the season.”