What are the limitations on an injured employee’s right to select his own doctor?

Q. While at work, one of our employees suffered what we believed to be a minor back injury. We sent him to a clinic, which determined that he could perform light-duty work. We offered him a light-duty assignment. Now the employee has gone to his personal physician, who has excused him from all work. The employee’s physician also has billed us for his services, since this was a work-related injury. We do not know how to respond to these differing opinions or whether we are obligated to pay for the employee’s personal physician’s services ...