Johnson has been diagnosed with a fractured tibia in his left leg, Jay Glazer of FOX Sports reports.
Johnson was knocked out of Sunday's game in San Francisco, after his left knee has hit by an opposing player's helmet. The initial diagnosis of a bone bruise indicated a short absence was in store, but Glazer's bombshell says otherwise. The Cardinals will explore if there's a chance that he can return at some point, but the running back corps could be down to David Johnson and Stepfan Taylor in the short term due to Andre Ellington's bout with turf toe.