Defensive back Grant Haley also has been restored from the COVID list to the practice squad.
With the moves, the Rams are down from 29 players earlier in the week to 23 on the reserve/COVID-19 list, including starting right tackle Rob Havenstein, outside linebacker Von Miller, safety Jordan Fuller and tight end Tyler Higbee.
The Rams (9-4) are scheduled to host the Seattle Seahawks (5-8) at SoFi Stadium on Tuesday after the NFL rescheduled the game from Sunday because of the Rams' coronavirus outbreak.
"Very excited to be able to get Jalen back. We know how important he is to our team from a leadership perspective and then a production perspective on the field, so that's really big to be able to get him back," Rams coach Sean McVay said Sunday. "Then there are some other guys who are trending in the right direction and hopefully we'll be able to get some good news on them today or tomorrow."
Rams defensive coordinator Raheem Morris said if Fuller, the defensive signal-caller, was unable to play against the Seahawks that Ramsey was among candidates (along with safety Taylor Rapp or rookie linebacker Ernest Jones) to take over the duties.
Ramsey was placed on the COVID list only hours before kickoff in a 30-23 victory over the division-leading Arizona Cardinals last Monday.