Watford will assess Juraj Kucka and Joao Pedro, who were both ruled out of last Saturday's win at Aston Villa.
Samir, who was substituted during that game because of a head injury, is available and Peter Etebo could return.
Conor Gallagher is available again for Crystal Palace, having been ineligible to face his parent club Chelsea.
Goalkeeper Vicente Guaita was unable to continue after half-time in that fixture because of a knee problem, making him a doubt for Wednesday.
MATCH FACTS
Head-to-head
- Crystal Palace won the most recent league meeting 1-0 at home on 7 March 2020 to end a six-match run without victory against Watford in all competitions.