The City Manager may designate, by letter filed with the Clerk of Council, any qualified administrative officer of the City to perform the duties of the City Manager during the temporary absence or disability of the City Manager. If such designation has not been made, and the City Manager is unable to perform such duties or to make such designation, the Mayor on an emergency basis may appoint an acting City Manager until the next Council meeting. Council may thereafter appoint any qualified administrative officer of the municipality to perform the duties of the City Manager until the City Manager shall return or the disability ceases.