Manchester United manager says his team must be wary of the threat that will be posed by Watford in Saturday's Premier League clash at Old Trafford.
Watford defeated United 3-1 at Vicarage Road in the reverse fixture.
Watford have won their last two games after a poor run of results.
"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," Mourinho said in Friday's press conference.
"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.”
Recalling United's defeat against Watford in their first meeting this season, Mourinho said: "I was very angry with the first goal. I was very angry because [Anthony] Martial had to leave the pitch with a very strong tackle – he had the possibility of a concussion, he didn’t play the next match but no foul [was awarded], it was a goal."
On the availability of Eric Bailly and United's plans for the summer transfer, Mourinho added: "Every team needs four central defenders. But we coped well without Eric. Now it’s time for Jones to be out and time for Eric to be in. Of course, we’re happy he played already that last match and he showed again security and understanding with the other guys, so we’re fine.
"We have a squad that, like every squad, needs changes but we know also that our squad has potential, our squad has good players. Some players will leave, some players will come but in a very natural way. Everything is balanced and I think our summer [activity] will be quite small."