Mattison (undisclosed) rode a stationary bike on the side during Wednesday's practice, Eric Smith of the Vikings' official site reports.
Mattison initially missed practice Monday and now seems unlikely to play in Friday's preseason game against the Chiefs. After that, he'll have 16 days to prepare for Minnesota's Sept. 12 opener against Cincinnati, gearing up for his familiar role as Dalvin Cook's backup. The Vikings used a fourth-round pick on Kene Nwangwu this spring, but he's a raw prospect in the first place and now has been out since mid-August with a hyperextended knee. If Mattison is unexpectedly slow to recover from his current issue, the Vikings can turn to Ameer Abdullah, Ito Smith or A.J. Rose for Week 1 backup snaps.