Profootballtalk.com reports that Tarvaris Jackson suffered a sprained MCL in the Vikings' preseason game Saturday night.

Jackson played through the injury for a few snaps Saturday before having to exit. The 25-year-old passer has been effective in the preseason, but he's had knee problems before so this is a concern. Jackson shouldn't need surgery, but it remains to be seen when he'll be back in action.

Source: Profootballtalk.com