The 49ers placed Mitchell (knee) on injured reserve Tuesday.
The transaction was fully expected after Mitchell was diagnosed with a MCL sprain in his right knee following his departure from Sunday's rain-soaked season-opening loss to the Bears. Though Mitchell is expected to avoid surgery to address the injury, he's likely to need approximately two months to recover from the sprained knee. Mitchell's absence for the next several weeks should pave the way for rookie third-round selection Tyrion Davis-Price, who was inactive Week 1, to dress on game days, but he still may find himself behind veteran Jeff Wilson and undrafted rookie Jordan Mason in the 49ers' backfield pecking order.