Worker's compensation laws vary by state. Without knowing in which state your company operates, I cannot answer your question with absolute certainty. However, I can say that in most states, if he has been returned to work by his primary physician or specialist without restrictions that would preclude him from safely doing his former job (i.e., without likely re-injury to himself or injury to others), the answer would be yes, you are required to give him his original job back--or to give him a job with the same pay level as he was earning before his injury occurred.