Watford head coach Walter Mazzarri has revealed Younes Kaboul will miss the midweek clash with West Brom and could be sidelined for the rest of the season.
The defender injured his hamstring in the 1-0 home win over Sunderland on Saturday and will be assessed on Monday.
"He's a very important player. It doesn't look good - he won't be available for Tuesday," Mazzarri told the club's official website.
"We haven't been very lucky with injuries this season and because of this, we should have more points than we do."
The Italian also feels they must work on their finishing ahead of Tuesday's visit of the Baggies, after they spurned a number of chances to kill off Sunderland.
Miguel Britos scored a 59th-minute winner to leave David Moyes' side rooted to the bottom of the Premier League but Mazzarri knows they must be more ruthless in front of goal against a well-drilled West Brom team.
"We had a really good game against Sunderland and I was very, very happy," he added.
"We must improve on the last pass and we need to improve our finishing. We could have closed the game before we did."
Watford go into the game 12th in the table, seven points clear of the relegation zone, with the win over Sunderland ending a poor run of results that had seen them claim just one point from their previous four Premier League outings.
Mazzarri still insists every game will be a 'cup final' until their survival is guaranteed, however, and is keen to focus his attentions on pitting his wits against Tony Pulis' side.
"Until the table says mathematically we are safe, then we are not," he added. "We don't even need to think about that - we need to think about the game against West Brom.
"We have 27 points to play for and we need to think about playing every game as a cup final."
Watch Watford's trip to Tottenham on Saturday. Coverage begins on Sky Sports 1 HD at 11:30am.