The Chiefs listed him as questionable and said they won't determine whether or not he will play until he is examined by the medical staff on Sunday. Cassel is recovering from an appendectomy that sidelined him last week.
He's been listed for limited participation this week, but reporters who saw Cassel early in Friday's practice noted he was throwing the ball with more velocity and appeared to be doing more with the offense in practice.
The Chiefs (8-5) must beat the Rams to remain alone in first place in the AFC West. Coach Todd Haley said a decision between Cassel and backup Brodie Croyle would probably not be made until just before the game.
Cassel sat out last week against the Chargers while the Chiefs, behind Croyle, had one of their worst offensive showings ever and lost 31-0.
John Clayton is a senior NFL writer for ESPN.com. Information from The Associated Press was used in this report.