"The initial diagnosis was that Vikings quarterback Tarvaris Jackson suffered a bruised right knee in Saturday's preseason game at Baltimore, but further tests revealed a sprain to his MCL, according to a person with knowledge of the situation.

Vikings coach Brad Childress was not available for comment Sunday, but it's reasonable to think the injury could keep Jackson out of the most important game of the preseason Saturday against the Pittsburgh Steelers.

Teams typically treat their third preseason game as a dress rehearsal for the regular season, giving starters extended playing time. Jackson's status for the preseason finale at Dallas on Aug. 28 also is unknown, but it's hard to imagine he would not be ready to play in the season opener Sept. 8 at Green Bay.

Jackson suffered the injury while scrambling in the first quarter of a 23-15 victory against the Ravens. Rather than slide to avoid contact, Jackson took on a hit by Ravens linebacker Ray Lewis and then safety Dawan Landry.

The Vikings had the day off Sunday. The team is expected to give anon Jackson today after practice at Winter Park."