Necessary precautions? Do you understand how random ACL/knee injuries are? Sam Bradford tore his yesterday landing on his knees and sliding, Brian Cushing tore his by getting hit from the outside. I tore both of mine by hits to the outside. It's hard to argue that Sam Bradford and Brian Cushing didn't take precautions and aren't healthy.
I think you're thinking of injuries like muscle cramps, sprains, pulls, and easily preventable injuries.