Jeffrey Schlupp is back in contention for Crystal Palace following his recovery from an ankle injury.
The full-back has returned to first-team training, but is not expected to start at Vicarage Road.
Provisional squad: Hennessey, Cavalieri, Speroni, Wan-Bissaka, Fosu-Mensah, Tomkins, Sakho, Kelly, Delaney, Jach, Riedewald, Van Aanholt, Souare, Schlupp, Townsend, Cabaye, Milivojevic, Loftus-Cheek, McArthur, Rakip, Lee, Zaha, Benteke, Sorloth.
Four Watford players have been struggling with a stomach virus in the build-up.
Defender Sebastian Prodl is among those who have been ill, while Gerard Deulofeu has also been absent from training with a throat infection.
Jose Holebas returns after missing the defeat against Huddersfield with a back injury. Younes Kaboul (foot) and midfielder Nathaniel Chalobah (knee) continue their rehabilitation.
Provisional squad: Karnezis, Janmaat, Prodl, Mariappa, Kiko, Holebas, Doucoure, Hughes, Capoue, Pereyra, Deeney, Gomes, Britos, Cathcart, Richarlison, Gray, Carrillo, Okaka, Kabasele.
Last season: Crystal Palace 1 Watford 0, Watford 1 Crystal Palace 1
Last five league matches: Watford L L D L L; Crystal Palace L W L D W
Top goalscorers (all competitions): Richarlison (Watford) 8; Luka Milivojevic (Crystal Palace) 10
Match odds: Watford 9-5 Draw 23-10 Palace 6-4