Have the MRI done yourself; then, as appropriate, apply for worker's compensation or sue your employer for compensation (you sue if worker's compensation is not available). You do not need your employer's permisson or consent for medical treatment, and the law does *not* require them to pay for it upfront: rather, IF medical examination shows a work-related injury, then you could seek worker's compensation and/or sue. So get the treatment you need; then figure out what compensation to seek.