The Red Devils head into the game looking to build on their 3-0 win over Leicester City last weekend and aiming to kick-start their bid qualify for the Champions League.
Manchester United are currently in sixth place in the Premier League table and 14 points behind leaders Chelsea after a stuttering start to life under the Portuguese coach at Old Trafford.
The Red Devils were beaten by Watford earlier in the season and will be looking to gain revenge in front of their home fans at Old Trafford.
However, Mourinho has warned his players that they must be at their best if they want to beat Walter Mazzarri’s men this weekend.
Speaking at his news conference on Friday afternoon, Mourinho said: “I know they are very difficult. They are very defensive but there are teams that are defensive and not well organised. That’s not Watford’s case.
“Walter [Mazzarri] is a very good coach, the team is very well organised and then they have this capacity of being dangerous on the counter-attack and at set-pieces with a very physical team.”
Manchester United finished fifth and won the FA Cup last season under Louis van Gaal.
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