Minnesota Vikings quarterback Sam Bradford was ruled out Sunday with a knee injury, and Case Keenum will start under center against the Pittsburgh Steelers, according to NFL Network's Ian Rapoport.
The Vikings later confirmed that Bradford was inactive.
ESPN's Chris Mortensen reported Friday that the Vikings were concerned about Bradford's knee after he experienced "swelling, pain and discomfort" following the team's Week 1 win over the New Orleans Saints.
Minnesota promoted Kyle Sloter from the practice squad to the 53-man roster Saturday, and he will serve as Keenum's backup.