Emp. walking to the belt controller & tripped on a turnbuckle & anchor. He fell face down on the floor. Emp. denied pain at the time of injury. He contin. to work & his left knee started hurting. Emp. was off on personal leave & notified the Safety Dept. on 12/8/10 that he was still having swelling & pain to his left knee. Emp. taken to doctor & placed on restrictions on 12/9/10.