Thomas has been dealing with back stiffness and hasn't fully practiced for about a week, Alec Lewis of The Athletic reports.
Thomas was taken in the third round of April's NFL Draft and is expected to provide key depth in the Vikings' secondary this season. His current injury is particularly notable because fellow safeties Josh Metellus (shoulder) and Jay Ward (concussion) are both currently working through injuries of their own. However, there's no indication at this point that Thomas is at risk of not being ready for Week 1 of the regular season.