Sam Bradford is coming off a career performance in the Vikings' season-opening thumping of the Saints. The 2010 first-overall pick completed 84 percent of his passes for 346 yards, three touchdowns and no turnovers. It was exactly the type of performance the Vikings would need from Bradford when they traveled to Pittsburgh to face the Steelers this Sunday.

Except that Bradford experienced "swelling, pain and discomfort" during the week, according to ESPN's Chris Mortensen, who added that the team remained hopeful that Bradford would play but had concerns too.

In addition to Bradford, who was listed as questionable on the injury report, the only other quarterback on the 53-man roster was veteran journeyman Case Keenum. Until Saturday, anyway; the team promoted rookie Kyle Sloter from the practice squad, waiving safety Antone Exum to make room for him.

Sloter, an undrafted free agent, played collegiately at Southern Miss and Northern Colorado. He signed with the Broncos in May but was released on Sept. 2. Two days later, Sloter was signed by the Vikings, which means he's had less than two weeks in Minnesota's offense.

During the preseason in Denver, Sloter completed 31 of 43 passes for 413 yards, three touchdowns, no interceptions and a 125.4 passer rating.

Vikings coach Mike Zimmer said Bradford is expected to play Sunday, though he wouldn't comment on reports that the quarterback had an MRI on his knee earlier in the week.

"I'm not going to talk about who's had MRIs or who hasn't had MRIs," Zimmer said on Friday, via the StarTribune.com. "Lots of guys have MRIs. I had one, two maybe, on my knee."

Bradford's injury is to his left knee, the same knee he twice required surgeries to repair a torn ACL in 2013 and 2014.

Pittsburgh is favored by six points, and while all eight CBSSports.com experts expect the Steelers to win their home opener, only four think they will cover.