Mack (hamstring) was placed on injured reserve Tuesday, Aric DiLalla of the Broncos' official site reports.
Mack injured his hamstring in Sunday's loss to the Chiefs, and he was not expected to recover in time to play Week 18 against the Chargers. His move to IR ensures he won't, while also creating room for cornerback Ja'Quan McMillian to be added to the active roster. Mack's season will end with him having appeared in eight games, two with the 49ers and six with the Broncos, seeing 16 carries for 84 yards and a touchdown. He also caught eight of his 10 targets for 99 yards and another touchdown.