"It's unfortunate," Rams coach Sean McVay said Tuesday.
McVay said Talib's recovery process and a timeline for his return would be predicated on what doctors discover during surgery Thursday.
"It depends on once you get in there because the specifics of what the severity is once you actually see what needs to be totally fixed," McVay said. "If there's something going on with his deltoid [ligament] then it ends up being a little bit longer."
"He's feeling good," McVay said. "I think it's a great representation of his toughness to even still have it be a chance that he's going to play. You look at what occurred and you talk about what that position requires and entails with the movement, so he's taking steps in the right direction."
Cornerback Nickell Robey-Coleman, who is used mostly in the slot, also can fill in on the outside.
The Rams' acquired Talib, a five-time Pro Bowl selection, and Peters, a two-time Pro Bowl selection, via trades over the offseason in an effort to upgrade their defense.
This season, Talib has seven tackles and two pass deflections.
Peters has four tackles, a pass deflection and intercepted a pass and returned it for 50 yards for a touchdown in a Week 1 victory over the Oakland Raiders. Peters has a league-best 20 interceptions dating to 2015.