Watford midfielder Ross Jenkins is hoping to return to contention for the game.
Jenkins injured his ankle in the recent 2-2 draw with Leeds and missed Saturday's home win over Barnsley, but could provide manager Malky Mackay with a boost.
Piero Mingoia was recalled to the starting line-up against Barnsley before being replaced in the second half by on-loan midfielder Danny Drinkwater, so Mackay is not short of alternative options.
Winger Matty Whichelow is nursing an ankle problem and defender Tom Aldred sustained a head injury in the same game. Both players could be added to the squad along with Michael Bryan, who has recovered from an ankle injury of his own. Midfielder Stephen McGinn (knee) remains a long-term absentee.
The Hornets must win and hope other results go their way if they are to keep their outside play-off hopes alive.
Leicester captain Matt Oakley is set to miss out.
Oakley scored a fine goal during the 3-2 defeat at Nottingham Forest on Good Friday, but lasted just a few minutes of the second half before coming off with a groin injury.
Japanese midfielder Yuki Abe replaced Oakley at the City Ground and could start in his place.
Manager Sven-Goran Eriksson must decide whether to keep faith with goalkeeper Chris Weale after his howler handed Forest victory or recall his Portuguese number two Ricardo.
Defender Sol Bamba faces a fortnight on the sidelines after suffering a hamstring injury during the defeat to Reading.
Bamba and striker Martyn Waghorn, who also has a hamstring problem, are the only other absentees.