According to ESPN.com's Courtney Cronin, the Vikings announced Saturday they'd signed Sloter off the practice squad and waived safety Antone Exum Jr. to make room on the roster.
ESPN's Chris Mortensen reported Friday the Vikings have "some concerns" after Bradford underwent an MRI Tuesday after experiencing "swelling, pain and discomfort" in his knee following the team's 29-19 win over the New Orleans Saints in Week 1.
Mortensen added the Vikings are "cautiously optimistic" Bradford will be able to play against the Steelers. The former No. 1 overall draft pick has been a limited participant in practice this week, per the team's official injury report.
Sloter was an undrafted free agent out of Northern Colorado in 2017. He signed with the Denver Broncos in May and went 31-of-43 with 413 yards, three touchdowns and no interceptions in the preseason before being waived Sept. 2.
If Bradford can't play against the Steelers, backup Case Keenum would likely get the start. Sloter would be Minnesota's No. 2 quarterback for the game.