The Rams placed running back Ronnie Rivers on injured reserve Wednesday, the team announced.
Rivers is out 4-5 weeks with a Grade 3 PCL sprain in his knee.
He has played 40 offensive snaps and 88 on special teams, getting 17 touches for 75 yards.
Starting running back Kyren Williams will not play Sunday, coach Sean McVay confirmed Wednesday, but the Rams still are evaluating the plan for Williams.
Williams injured his ankle in the fourth quarter Sunday in a game he rushed for a career-high 158 yards and a touchdown. He has 97 carries for 456 yards and six touchdowns in six games this season and 13 catches for 105 yards and a touchdown.