Yep. Rotoworld:
Trey Sermon is a healthy inactive for Week 1 against the Lions.
So much for Sermon being a usable RB3/FLEX option for the opener. This is a big surprise, as the 49ers are rolling with Raheem Mostert, JaMycal Hasty, and Elijah Mitchell in the backfield. It's a huge boost to Mostert's Week 1 status as a rock-solid RB2. Also inactive for the 49ers are CB Emmanuel Moseley, DT Javon Kinlaw, CB Josh Norman, and OL Aaron Banks.