The Iceland international is back at Vicarage Road on loan from Rangers and cannot face his parent club.
Boss Malky Mackay will check on the fitness of Arsenal loanee Henri Lansbury, who limped out of Saturday's 2-0 defeat at Newcastle with a hip injury.
The Hornets have been boosted by the return of club captain Jay DeMerit, who was on the bench at St James' Park.
The USA centre-half has been sidelined since August after needing surgery on the eye he scratched while removing a contact lens.
Teenage midfielder Ross Jenkins is therefore the only definite injury absentee following his recent back operation.
Steven Reid and Matthew Connolly are expected to be missing from the QPR squad.
On-loan Blackburn midfielder Reid is still struggling with a hamstring problem and defender Connolly has a pelvic injury.
Rangers picked up no fresh knocks at the weekend but boss Jim Magilton is expected to make changes following the 5-1 mauling by Middlesbrough.
Damion Stewart, Peter Ramage and Tommy Williams will all push for starts in a shell-shocked defence.
"We've got just a few hours to think about it and we'll go to Watford aiming to put the wrongs of that performance right," said Magilton.
Angelo Balanta (groin) is close to returning but Gavin Mahon, Martin Rowlands and Lee Cook (all knee) are long-term absentees.
Sporting Life