Soares has missed the club's last four league games due to a foot injury, while Forster was replaced in the England squad by Sunderland's Jordan Pickford after picking up an unspecified knock that ruled him out of games against Scotland and Spain.
Pierre-Emile Højbjerg also returned from international duty earlier than planned, missing Denmark's World Cup 2018 qualifier with Czech Republic. The midfielder is expected to feature against Jurgen's Klopp's side.
Southampton manager Claude Puel added at his press conference on Thursday he is hopeful both Ryan Bertrand and Dusan Tadic will be fit to start, although he is holding off on making a final decision until after the club's final training session of the week.
"I don't know for sure yet because I cannot see all of the players, but we will see in the training session," Puel said. "I think we can recover many players. I think it is okay for Fraser and Pierre. They have some injuries in the last week but they should be fine.
"Ryan is OK and Tadic had an injury to his nose, but he spoke with the medical team already and should be fine for Saturday's game."
He added: "Cedric will come back, and Shane Long has come back into training sessions, but it is too soon for this game. But we will see next week. Targett is still injured, but for the other players it's okay."
Liverpool currently lead the Premier League, a point ahead of second-placed Chelsea, and are currently on a 12-game unbeaten run.
Southampton have lost their last three games in all competitions and sit 10th in the league ahead of kick-off.