The Municipal Manager may designate, by letter filed with the Clerk of Council and approved by motion of the Council, any qualified administrative officer of the municipality to perform the Manager's duties during the Manager's temporary absence or disability. If such designation has not been made, and the Municipal Manager is unable to perform the Manager's duties or make such a designation, the Council shall declare by ordinance or resolution, which shall be immediately effective, that a state of disability exists and shall appoint any qualified administrative officer of the municipality to perform the duties of the Municipal Manager until the Manager shall return or the Manager's disability ceases.