In my law practice, I often receive calls from employees inquiring about wrongful termination issues because they lost their job while on leave for health reasons. The employer, of course, may have legitimate reasons for terminating an employee on medical leave. The employer may need to fill the empty position to meet pressing work demands, or may be unhappy about the past work performance of the absent worker. While these motives are understandable, there are reasons why firing an "on leave" employee should be avoided if possible.
Document before termination. If possible, document infractions (that may lead to termination) before you terminate the employee. For example, write down in memo form instances of employee misconduct or poor performance, then meet with your employee to discuss the matter. Present the memo and ask your employee to sign same to acknowledge receipt, keeping a signed copy to place in the employee's personnel file. In the memo, advise the employee that any further infraction could lead to discipline, which could include termination. Now you have "documented" the event.