Marvin Zeegelaar will serve a three-game ban after losing an appeal against his red card issued against Burnley on Saturday.
The Watford defender was sent off at Turf Moor, following a two-footed tackle on Steven Defour in the 39th minute.
Burnley went on to win the match 1-0, with Scott Arfield scoring the winner on the stroke of half-time.
Zeegelaar will sit out Premier League fixtures against Crystal Palace, Huddersfield and Brighton.
The Hornets tweeted: "#watfordfc will be without Marvin Zeegelaar for the next three games after the club's appeal against his red card at Burnley on Saturday proved unsuccessful."
Watford boss Marco Silva insisted after the match that referee Lee Probert had been wrong to show Zeegelaar a straight red card.
Silva said: "There was good competition between everybody then, after one decision, the referee made a big difference in the match, a big influence, and it was a harsh decision for me.
"It's not a red, that changed everything, and after two or three minutes they scored.
"The referee never had control of the match and he lost it with the moment when he made the mistake.
"I understand I can make mistakes and so can our players, and the referee can too, but he made a big mistake and that had a big influence."