When an employee is sick or has been injured, and the employee has no sick days or injury pay left, and extended sick or injury pay has not been granted, then the employee may apply for a Leave Without Pay. The request must be accompanied by the Statement of Attending Physician verifying the necessity for such leave. The leave may be granted for periods of thirty (30) days or more, depending on the condition of the employee, not to exceed two (2) years from the date the employee's sick pay or injury pay has been exhausted, except as provided elsewhere herein, or unless by mutual agreement this period is extended in writing.