We'll have more from coach Mike Zimmer after this morning's practice, but John Sullivan's back injury is starting to look like more of a concern after the veteran center wasn't at practice again this morning.

Sullivan missed three weeks of practice and two preseason games that he would have played in. The team has said the injury is not serious, but one has to start wondering about that now that the Vikings have moved into preparing for the Sept. 14 regular season opener at San Francisco.

The Vikings, however, do have an extra day with the game being on Monday Night Football. But Sullivan hasn't been seen at practice since the back spasms surfaced.

In other injury news, fullback Zach Line and defensive tackle Shamar Stephen aren't practicing during what's expected to be a short practice without pads. Practice squad linebacker Brian Peters also wasn't practicing during the portion of practice open to the media.