Cowboys left guard Ronald Leary missed the Wednesday morning walk-through because of a left knee problem. Leary who said he expects to practice Thursday will undergo an MRI. Leary has a chronic condition in his left knee called osteochondritis dissecans (os-tee-o-kohn-DRY-tis DIS-uh-kanz) a joint condition where a piece of cartilage along with a thin layer of the bone beneath it comes loose from the end of a bone. Coach Jason Garrett said this current knee problem isn't related to that. "We don't think this is a serious thing" Garrett said. "We'll get the MRI and see what it looks like and we'll move forward." David Arkin replaced Leary as the first-team left guard and Dennis Godfrey took over at guard for the second and third teams.