Both defenders went off injured during the Hornets’ 2-0 win at Southampton last weekend, right-back Femenia with a head knock and centre-back Kaboul carrying a hamstring problem.
Adrian Mariappa could come in alongside Christian Kabasele at the heart of the back four after he replaced Kaboul on 61 minutes at St Mary’s last Saturday.
Sebastian Prodl, Craig Cathcart and Mauro Zarate are still injured and Miguel Britos is suspended for Marco Silva’s men.
Provisional squad: Gomes, Karnezis, Janmaat, Kabasele, Wague, Mariappa, Femenia, Holebas, Zeegelaar, Capoue, Hughes, Chalobah, Doucoure, Cleverley, Watson, Carrillo, Pereyra, Deeney, Success, Richarlison, Okaka, Gray.
Paul Huntington says Preston's play-off hopes this season hinge on them getting the balance right on and off the pitch.