Keita, 27, is currently sidelined with a muscle injury and is yet to feature in a competitive match this season.
Oxlade-Chamberlain, 29, is also yet to make an appearance this campaign after suffering a hamstring injury in pre-season.
Liverpool were required to submit their squad for the group stages of the Champions League by midnight on September 2.
The Reds have named 24 players as 'List A', including new signing Arthur Melo.
Meanwhile, 'List B' players – those born on, or after, 1 January 1998 and have been eligible to play for the club for any uninterrupted period of two years since turning 15 – are unlimited and can be confirmed the midnight before any game.
The Reds swooped for Arthur on the final day of the summer transfer window, signing the midfielder on loan from Juventus.
He was brought in to provide much-needed cover in midfield for Jurgen Klopp, who is also currently without injured duo Jordan Henderson and Thiago Alcantara.
Arthur has been brought straight into Liverpool's Champions League squad, with Keita and Oxlade-Chamberlain missing out due to injury.
Speaking ahead of Saturday's 0-0 draw with Everton, Klopp confirmed Thiago was close to returning for the Reds but said Oxlade-Chamberlain and Keita would be out for the foreseeable future.
"It's a muscle injury, yeah," Klopp said about Keita.
"Ox is a muscle injury and they will be out for a while."
Keita and Oxlade-Chamberlain could be brought back into Liverpool's Champions League squad in January, when teams are next allowed to make changes.
Liverpool travel to face Italian side Napoli in their first Group A match on Wednesday, with Ajax hosting Rangers in the other game in the group.
Last season, Liverpool reached the final of the Champions League - losing 1-0 to Real Madrid at the Stade de France in Paris.
Liverpool's Champions League squad:
Goalkeepers: Alisson, Kelleher, Adrian
Defenders: Van Dijk, Gomez, Konate, Matip, Phillips, Alexander-Arnold, Robertson, Tsimikas, Ramsay
Midfielders: Fabinho, Thiago, Henderson, Milner, Arthur, Bajcetic
Forwards: Salah, Firmino, Jota, Diaz, Nunez, Carvalho
List B: Elliott, Jones