Sims has made 14 tackles for Detroit (0-2) this season. He was injured in Sunday's loss to Minnesota.
Sims has not missed a game since the Lions drafted him three years ago. He is the only player on Detroit's active roster selected by former general manager Matt Millen between the 2002-06 NFL drafts.
Schwartz says he does not know how long Sims will be out, adding Sims does have more than a day-to-day injury. The Lions host the Redskins this weekend.