Usually a very bad ankle sprain would take more than a month to fully recover especially if it was not immobilized properly. It would take around 6 to 8 weeks to recover provided that a proper supporting splint or brace was applied throughout the recovery period. If it is not than most of the time the recovery would be delayed. However it would be best to check your ankle joint stability by an orthopaedic surgeon and to  get an ankle mri done to ascertain which ligament is injured and what degree of injury does it have to prognosticate your recovey. From there the doctor can determine whether surgical interventiin is needed. 

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