Mitchell (knee) has been ruled out for Thursday's game against the Titans, Cam Inman of The San Jose Mercury News reports.
Jeff Wilson figures to start and handle the lead role for a third straight week, while Trey Sermon (knee) could soon be available after the Niners designated him to return from IR on Wednesday. It remains to be seen if the rookie can play Thursday night, though he'll likely have a small role even if he does. Mitchell, meanwhile, will hope to make it back to practice next week ahead of a Week 17 matchup with the Texans (on Sun., Jan. 2)