State workers' compensation systems establish technical and often tricky rules in this area. Often, you have the right to ask for another doctor at the insurance company's expense if you clearly state that you don't like the one the insurance company provides, although there is sometimes a waiting period before you can get a second doctor. Also, if your injury is serious, you usually have the right to a second opinion. And in some states, after you are treated by an insurance company's doctor for a certain period (90 days is typical), you may have the automatic right to transfer your treatment to your own doctor or health plan, while the worker's compensation insurance company continues to pay the bill. Because the insurance company is paying, don't hesitate to go to a doctor who specializes in your injury or illness -- even if the cost is great.
To understand your rights, get a copy of your state's rules or, if necessary, research your state workers' compensation laws and regulations in the law library.