"The belief ... was that this was a one-week injury for Sam Bradford," Ian Rapoport of NFL Network reported on Good Morning Football. "... I'm told the ACL is fine. The other ligaments are fine. This really is a swelling and discomfort issue after taking a shot to that knee last week.
"The only thing is, they really don't know how his knee is going to respond to treatment, how his knee is going to handle getting worked on all week and when he'll be able to really fully bend it like he needs to. They think it's going to be one week. They think he'll be back under center next week. But until you get on a couple days and see how the treatment takes hold, there's really no way to know for sure."
Tom Pelissero of NFL Network later reported Bradford is believed to have a bone bruise.
An MRI last week showed no structural damage to Bradford's knee. He sat out Sunday's 26-9 loss to the Pittsburgh Steelers.
Case Keenum started in Bradford's place, throwing for 167 yards on 20-of-37 passing in a disappointing effort. The Vikings managed just 237 yards of offense a week after they lit up the New Orleans Saints for 470. Bradford threw for 346 yards and three touchdowns on 27-of-32 passing in that contest.
"I'm disappointed. I'm a competitor," Keenum said after the game. "I like to win, and any time we don't, I take it really hard.
"I want to fight for those guys in that locker room, and I feel like I can play better. I feel like we showed some good things but obviously didn't get off to a great start and shot ourselves in the foot quite a few times. When other things aren't clicking, that's unfortunate."
On Sunday, the Vikings will host a Bucs team coming off a dominant 29-7 win over the Chicago Bears in Week 2.