Appointment of managing director

Hello Members,

Please give your opinion in the following matter:

Section 316(2) states that a unanimous board resolution is required in case a public limited company wants to appoint a person as managing director who is already a managing director in any other company.

Now I want to know that when the unanimous board resolution is required? Can it be passed after the appointment of the said person as managing director or prior approval of board is required?

Thanks.