The Brazilian missed Friday night's 5-0 win over Huddersfield Town due to a small groin tear and has now failed to prove his fitness in time to be named in Jurgen Klopp's starting XI for tonight's showdown.
Firmino's compatriot Fabinho does return to the side, though, having overcome the head injury which ruled him out of Liverpool's last game.
Trent Alexander-Arnold is a surprise exclusion from the starting XI as he is replaced at right-back by Gomez, who makes his first start in any competition since December.
Barcelona, meanwhile, welcome talisman Lionel Messi back into their side after he was rested from the start at the weekend, with the Argentine looking for his 25th goal against English opposition - and his first against Liverpool.
Barcelona: Ter Stegen; Roberto, Pique, Lenglet, Alba; Rakitic, Busquets, Vidal; Messi, Suarez, Coutinho
Subs: Semedo, Arthur, Dembele, Cillessen, Malcom, Alena, Umtiti
Liverpool: Alisson; Gomez, Matip, Van Dijk, Robertson; Milner, Fabinho, Wijnaldum; Keita, Salah, Mane
Subs: Lovren, Firmino, Henderson, Mignolet, Shaqiri, Origi, Alexander-Arnold
Follow Sports Mole's live in-depth coverage of tonight's match by clicking here.