A league source tells us that Vikings quarterback Tarvaris Jackson has undergone an MRI to gauge the extent of the damage he suffered today during a training-camp scrimmage.
Per the source, Jackson suffered an MCL sprain.
Initial word is that it's only a Grade I sprain, and that Tarvaris might be day-to-day.
If it's Grade II or worse, however, Jackson likely would miss multiple weeks -- which likely would make Sage Rosenfels the Week One starter by default.
Fantasy Impact: