PITTSBURGH -- Steelers running back James Conner is out for Sunday's game against the Oakland Raiders with an ankle sprain.

Coach Mike Tomlin said Tuesday that the injury is "more significant" than the team originally thought. Tomlin classified the injury as a lower leg contusion after last week's 33-30 loss to the Los Angeles Chargers.

The Steelers (7-4-1) will roll into Oakland with rookie Jaylen Samuels, veteran Stevan Ridley and Trey Edmunds, who was promoted from the practice squad for depth. This week's practices will determine how Tomlin distributes the workload.

"Sometimes the division of labor is revealed to you through that work," Tomlin said. "We've got a great deal of confidence in Ridley; we've got a great deal of confidence in Jaylen -- particularly as of late with Jaylen. He's a guy that's been on the rise in recent weeks. ... Trey's a guy who's played some pro football. We were excited about getting him on our practice squad when we acquired him. We'll put him in uniform and give him an opportunity to be a contributor as well."

Conner was hurt on a tackle late in the fourth quarter on a 10-yard screen pass. Samuels finished the drive and caught a 10-yard touchdown pass.

After a rough two-week stretch that included a crucial fumble in Denver, Conner got going Sunday with 60 rushing yards and two touchdowns on 15 carries. He added 14 receiving yards on three catches.

Conner is among the league leaders with 12 rushing touchdowns.

Ridley, who has a 1,000-yard season from his days with the New England Patriots, has 56 rushing yards on 18 carries as a backup this season.

Samuels, a fifth-round pick out of NC State, has 31 rushing yards on 12 carries but has produced as a pass-catcher, with seven receptions for 54 yards and two touchdowns.

Wide receiver Antonio Brown said after the game that he doesn't like to see teammates go down but "every guy in a helmet is upholding the standard, and anyone can be the reason we win."

The team also announced that receiver Justin Hunter was placed on the reserve/injured list.