Brazil international Firmino missed last week's 2-1 win over Burnley at Anfield with a groin injury and manager Jurgen Klopp confirmed the forward may only return to training on Friday or Saturday.
He said: "[Roberto] Firmino didn't train with team so far, but should either today or tomorrow."
Captain Jordan Henderson remains on the sidelines with a foot problem whilst fellow Englishman Daniel Sturridge is also ruled out due to a troublesome hip issue.
Striker Divock Origi is another facing a battle to be fit after picking up an unspecified injury and the manager says they must not rush the Belgian back into action.
Centre-back Dejan Lovren is fully fit after playing 75 minutes for the Under-23s on Monday and is expected to return to the starting XI.
Provisional squad: Mignolet, Clyne, Lovren, Matip, Milner, Can, Lallana, Wijnaldum, Mane, Firmino, Coutinho, Karius, Alexander-Arnold, Moreno, Klavan, Gomez, Lucas, Stewart, Origi, Woodburn, Wilson.