As Darkane already stated, this kind of stuff happens to ALL teams. We just don't pay much attention to it when it doesn't involve OUR guys.
Football is a violent sport, and even working out for it causes strain on muscles that aren't created to handle that kind of stress over and over.
Look at the injury to Jordy last preseason. No one even HIT him, and he tore up his knee. If he had been hit, you might understand that kind of injury. But it just happened that he landed wrong or turned wrong, and WHAM! Out for the year.