NFL: Players call it quits in prime of careers
49ers LB Patrick Willis' toe injury will require season-ending surgery
49ers among biggest hit by early retirements of Borland, Anthony Davis, Willis
Patrick Willis out for rest of season - ABC7 Chicago
49ers left guard Mike Iupati leaves with concussion - NBC Sports
Patrick Willis Explains Decision to Retire from NFL
Patrick Willis will be game-time decision for 49ers – The Mercury News
San Francisco 49ers: Can Chris Borland Replace Patrick Willis?, News, Scores, Highlights, Stats, and Rumors