Scarbrough (undisclosed) has been unable to practice since Monday, Dave Birkett of the Detroit Free Press reports.
Scarbrough entered training camp as the favorite for the No. 3 running back job, potentially serving as a short-yardage replacement for the lead duo of Kerryon Johnson and D'Andre Swift. The missed practice time could impact Scarbrough's bid for a Week 1 role, especially with Jonathan Williams reportedly looking good at camp. The Lions also have Ty Johnson and fifth-round rookie Jason Huntley battling for RB spots at the back end of the roster.