There are many instances that you wouldn't need an attorney to file your injury claim. Generally speaking, as long as the insurance company accepts the liability and pays out your damages in full, there is no reason to involve a lawyer.
However, it is recommended to hire an attorney in the following situations:
If you are not sure if you are eligible to file a claim without an attorney
If the insurance company is not willing to accept liability
If there are substantial damages
If you are injured and need medical treatment