Watford interim head coach Hayden Mullins could have Christian Kabasele and Roberto Pereyra back in contention for the Premier League match against Crystal Palace.
Defender Kabasele (hamstring) and midfielder Pereyra (thigh) are both in full training again, having been absent since the win at Norwich before the international break.
Centre-back Craig Dawson is stepping up his recovery from a head wound, while Daryl Janmaat (knee), Tom Cleverley (heel), Danny Welbeck (hamstring), Sebastian Prodl (knee) and Jose Holebas (ankle) all continue their own rehabilitation.
Cahill (knee) and Dann (ankle) missed the 1-0 midweek win against Bournemouth with Mamadou Sakho deputising, but the the former Liverpool was sent off for a high challenge on Adam Smith on just his second league start of the season.
Sakho therefore is suspended and Cheikhou Kouyate will step in if needed, but defenders Joel Ward (knee), Patrick Van Aanholt (hamstring) and midfielder Max Meyer (illness) are ruled out.
Watford provisional squad: Foster, Mariappa, Masina, Cathcart, Kiko, Doucoure, Hughes, Sarr, Capoue, Deulofeu, Deeney, Gomes, Foulquier, Chalobah, Quina, Dele-Bashiru, Gray, Success, Kabasele, Pereyra
Crystal Palace provisional squad: Guaita, Hennessey, Henderson, Tomkins, Cahill, Kelly, Dann, Townsend, Milivojevic, Kouyate, McArthur, McCarthy, Riedewald, Camarasa, Schlupp, Zaha, Ayew, Benteke, Wickham.