Weddle’s return to the Rams was announced by his agent, David Canter, on Wednesday.
Fuller, the Rams’ defensive signal-caller, suffered an ankle injury that will require season-ending surgery in Los Angeles’ overtime loss to the San Francisco 49ers on Sunday.
The Rams also are dealing with two other key injuries in their secondary. Safety Taylor Rapp, who grabbed his fourth interception of the season against the 49ers, has entered the concussion protocol and cornerback Darious Williams suffered a shoulder injury in the game.
The NFC West-champion Rams host the Arizona Cardinals in a wild-card round playoff game Monday night (ESPN, 8:15 p.m. ET).
Weddle, 37, retired after the 2019 season, in which he started all 16 games for the Rams. He was a team captain and was the defensive signal-caller.
A six-time Pro Bowl selection and two-time All-Pro, Weddle has 29 interceptions, including four returned for touchdowns, 8 forced fumbles, 7 fumble recoveries, 9.5 sacks and 98 pass deflections in 13 seasons.
He spent his first nine seasons with the Chargers, who selected him in the second round of the 2007 draft, and three seasons with the Baltimore Ravens before joining the Rams in 2019.
ESPN’s Lindsey Thiry contributed to this report.