PITTSBURGH — For the second year in a row, the Vikings will use their second starting quarterback of the season in Week 2. Only this time, it will be Sam Bradford exiting the lineup rather than entering it.

Bradford won't play for the Vikings on Sunday against the Steelers, sitting out because of a left knee injury that limited him in practice all week. Coach Mike Zimmer said Friday he expected Bradford to play on Sunday, but the Vikings proceeded with caution through the weekend, opting to test Bradford's knee in a pregame workout.

With offensive coordinator Pat Shurmur, quarterbacks coach Kevin Stefanski and head athletic trainer Eric Sugarman watching, Bradford threw a few passes off dropbacks, but didn't do much to test his knee in a brief workout. Keenum and Sloter emerged from the locker room for pregame warmups with the rest of the team, but Bradford wasn't seen on the field.

The quarterback's issues are with the same knee he had surgically repaired twice in 2013 and 2014. An MRI this week reportedly showed no structural issues with Bradford's ACL, and Bradford was only hit twice in the VIkings' win over the New Orleans Saints on Monday night, during which the quarterback completed 27 of his 32 passes for 346 yards and three touchdowns.

Nonetheless, he was listed as questionable for the game, as the Vikings added Kyle Sloter from their practice squad on Saturday to give themselves two healthy quarterbacks in the event Bradford couldn't play.

Keenum went 4-5 as a starter for the Rams last season, helping the team to a 3-1 start before the Rams lost four straight games. He completed 60.9 percent of his passes last year, throwing nine touchdowns against 11 interceptions before giving way to Jared Goff.

Sloter, whom the Vikings signed on Sept. 2 before the Broncos could get him to their practice squad, will back up Keenum on Sunday. He completed 31 of his 43 passes for 413 yards and three touchdowns in the preseason.

Linebacker Anthony Barr and cornerback Xavier Rhodes, who were both listed as questionable for the game with hamstring and hip injuries, respectively, will both play.

Also inactive for the #Vikings in Pittsburgh: CB Tramaine Brock, WR Rodney Adams, DT Jaleel Johnson, DE Tashawn Bower, G Danny Isidora and OT Aviante Collins.