The Seahawks were also without tight end Gerald Everett, who remains on COVID-19/reserve and missed his second straight game.
Carson was listed as questionable after missing practice Tuesday and Wednesday because of what coach Pete Carroll described as a recurring neck issue that flared back up this week. Carson was still sore on Thursday morning.
Alex Collins got the bulk of the work in Carson's absence. He gave the Seahawks a spark last weekend in their win over the San Francisco 49ers, with his 28-yard catch kick-starting their first touchdown drive after five straight three-and-outs to begin the game.
Collins finished with 78 yards and a touchdown on 12 touches.
With Rashaad Penny on injured reserve for at least two more games, Seattle's other available tailbacks against the Rams were DeeJay Dallas and Travis Homer, who are usually used in change-of-pace situations.
Right tackle Brandon Shell and defensive end Benson Mayowa were active after missing the past two games. Defensive end L.J. Collier was also active after Seattle's 2019 first-round pick was a healthy scratch in three of the first four games.