Your employer can provide you with light duty papeprs for a non-related work injury and then later tell you that you cannot have light duty at work unless the injury you sustained is work related. Whether or not your employer can refuse to reasonably accomodate your ankle sprain sustained at home while you recover from the injury is supect for light duty assignments at the workplace.There is a Federal Law called the "Americans with Disabilities Act" that requires employers to reasonably accomodate their employees with certain disabilities in the work place. Whether or not you sprained ankle falls into a disability (albeit temporary) that needs to be accomodated temporarily with light work needs to be looked into by you.You should have a meeting with your supervisor or human relations department if you have one about your request for temporary light duty.