Mattison (undisclosed) didn't practice Monday, Courtney Cronin of ESPN.com reports.
Mattison may have been injured in the Vikings' second preseason game, as he logged just two snaps and hasn't practiced since. He did watch Monday's practice from the sideline, whereas some of the players with more serious injuries weren't present at all. Assuming he makes it back on the practice field soon, Mattison is locked in as Minnesota's No. 2 back behind Dalvin Cook ahead of a Sept. 12 opener against Cincinnati. Last year, Mattison averaged 4.5 carries and 0.7 targets in the 10 full games he and Cook played together.