Your undeclared employee can apply to the court for registration of employment relations. In such case, upon rendering decision, the court will oblige you to pay salaries to employee for the entire period of his/her work. The fact that you previously paid salaries will not affect its payment by the court decision. In addition, you will have to pay taxes and social security contributions.
The court's decision on registration of labor relations with employee is basis for imposing a fine without conducting audit.
This means that you will pay twice for the same work and also receive a fine!