The 49ers placed Odum (knee) on injured reserve Saturday, Matt Barrows of The Athletic reports.
Odum popped up on Thursday's injury report due to a knee injury, and it appears serious enough to warrant a multi-game absence. He'll be required to miss at least the next four regular-season games, making Week 18 against the Cardinals on Sunday, Jan. 5 the earliest he could return. Tashaun Gipson and Malik Mustapha will serve as the 49ers' backup safeties behind Ji'Ayir Brown and Talanoa Hufanga (wrist) due to Odum's injury.