By letter filed with the City Clerk the City Manager shall designate, subject to approval of the Council, a qualified City administrative officer as acting City Manager to exercise the powers and perform the duties of City Manager during his/her temporary absence or disability. During such absence or disability, the Council may revoke such designation at any time and in such event, or in the event the City Manager shall fail to make such designation, it may appoint another officer of the City to serve until the City Manager shall return or his/her disability shall cease.