Dejan Lovren will miss Premier League leaders Liverpool's clash with bottom-placed Watford.
The defender has a hamstring problem, leaving boss Jurgen Klopp with just two fit centre-backs in Virgil Van Dijk and Joe Gomez.
Klopp could make changes against the struggling Hornets after the Reds' midweek exertions in the Champions League.
New Watford boss Nigel Pearson should have defender Craig Dawson available again following a head wound.
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.
