Employee stepped on a small rock, twisting his R. knee. This was on 10/6/09 (last day of his rotation). He went on 4 days off. He returned to work on 10/11/09 & worked the next 2 days. On 10/13/09 he came to work stating his knee is not feeling any better. We took him to doctor, and he was put on some work restrictions, which we were able to accomodate.