Klopp could make changes against the struggling Hornets after the Reds' midweek exertions in the Champions League.
Midfielder Roberto Pereyra will be monitored after his return to action from a thigh problem in last weekend's draw against Crystal Palace.
Left-back Adam Masina faces a fitness test on an unspecified problem, but Jose Holebas (ankle) remains sidelined, while Danny Welbeck (hamstring), Tom Cleverley (heel), Daryl Janmaat and Sebastian Prodl (both knee) continue their own rehabilitation.
Liverpool provisional squad: Alisson, Alexander-Arnold, Van Dijk, Robertson, Henderson, Wijnaldum, Oxlade-Chamberlain, Salah, Firmino, Mane, Adrian, Gomez, Milner, Lallana, Keita, Shaqiri, Origi.
Watford provisional squad: Foster, Masina, Cathcart, Kiko, Kabasele, Doucoure, Pereyra, Deulofeu, Deeney, Sarr, Gomes, Mariappa, Foulquier, Chalobah, Hughes, Gray, Success, Dawson.