A monitoring apparatus for a doctoring comprises a vibration sensor which is individual and is attached at a discrete location of a doctor blade arrangement, the at least one vibration sensor converting a mechanical vibration of the doctor blade arrangement to an electrical signal, the mechanical vibration being caused by the doctor blade in response to a scraping operation of a rotating roll which is in contact with a moving web. A data processing unit receives the electrical signal carrying information on the vibration, compares said vibration with a reference of at least one previous measurement of a same grade of the web, and start one or more preventive actions in order to avoid a drop-through in the case said vibration exceeds at least one boundary of the reference.