Leicester captain Matt Mills will miss the game through suspension.
The centre-half begins a three-match ban after he was shown a straight red card for a two-footed lunge on Birmingham's Morgaro Gomis during the 2-0 defeat at St Andrews on Sunday.
His absence means manager Sven-Goran Eriksson has to break up a back four that had previously kept four successive clean sheets.
"It is a big blow to lose Matt because, as we know, for four-and-a-half games the goalkeeper and the defence have been absolutely fantastic," said Eriksson, who has no new injury worries to contend with.
Lee Peltier could partner Sol Bamba in the centre of defence with John Pantsil coming in at right-back - as at St Andrews following Mills' dismissal.
However, a more likely scenario is Sean St Ledger, who was not on the bench on Sunday following his exploits with the Republic of Ireland, getting a chance to impress in a like-for-like switch for the City skipper.
Watford boss Sean Dyche will be without injured defender Martin Taylor when they visit Leicester.
The 31-year-old left the pitch early in the 2-0 defeat to Crystal Palace with a collarbone injury, and Dyche has confirmed the former Birmingham player will be out for "weeks, not days".
Carl Dickinson completed 90 minutes of Saturday's 2-0 home defeat after recovering from illness.
Fellow defender Lee Hodson is available for selection after shaking off a knee injury, and after failing to make the squad against the Eagles he could earn a place in a bid to shore up Dyche's leaky defence.
Midfielder Stephen McGinn (knee) is the only absentee as the Hornets search for their second away win of the season at the expense of Sven-Goran Eriksson's Foxes.
On-loan Wolves winger Michael Kightly is set to make his second appearance for the club, and Dyche told the Watford Observer: "He is a good player to have because he does have a few different options in his locker.
"He is predominantly a wideman but can play behind the striker, in the hole or at the top of a diamond."