Minnesota Vikings quarterback Sam Bradford was ruled out Sunday with a knee injury, and Case Keenum started under center against the Pittsburgh Steelers.

After the Vikings' 26-9 loss to the Steelers, head coach Mike Zimmer updated Bradford's status, telling reporters: "Sam is fine. He might play one game from now, he might play six weeks from now. Either way, he's fine."

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 served as Keenum's backup.

Bradford was coming off one of the best games of his NFL career, as he threw for 346 yards and three touchdowns against the Saints.

The 29-year-old Keenum is 9-15 in his career as a starter. He went 4-5 for the Los Angeles Rams last season, throwing for 2,201 yards and nine touchdowns against 11 interceptions.

Keenum completed 20 of 37 passes for 167 yards with no touchdowns and no interceptions.

If Bradford remains out going forward, wide receivers Stefon Diggs and Adam Thielen and tight end Kyle Rudolph will take a hit from a fantasy perspective, while rookie running back Dalvin Cook could see additional touches.