With AP NFL Offensive Player of the Year Christian McCaffrey (PCL) landing on the Injured Reserve list and third-year running back Jordan Mason (high ankle sprain) expected to follow, rookie Isaac Guerendo is primed to make his first-career start on Sunday against the Chicago Bears. His expanded role is one of few changes happening within the 49ers running back corps. Since the start of the week, the 49ers have elevated veteran Patrick Taylor Jr. from the practice squad to the 53-man roster and claimed former New York Jets running back Israel Abanikanda off waivers.