The 49ers placed Bethune (knee) on injured reserve Saturday, Cam Inman of The San Jose Mercury News reports.
Bethune sprained his MCL during the 49ers' Week 11 loss to the Seahawks. Now that he's on IR, Bethune will be forced to miss at least the next four games, and the earliest he could return is Week 16 against the Dolphins on Sunday, Dec. 22.