San Francisco 49ers nose tackle Glenn Dorsey has a torn left biceps muscle and will undergo surgery, a person with knowledge of the injury said Saturday. Dorsey left Friday's practice with the injury. Losing Dorsey would be a huge blow 11 months after 2013 starting nose tackle Ian Williams went down with a season-ending ankle injury in a Week 2 loss at Seattle. Mike Purcell, an undrafted free agent last year, could be an immediate option to fill the void left by Dorsey as San Francisco gears up for its preseason opener Thursday at Baltimore. More...