If the employee has not informed his employer of his sickness, he may not benefit from the protection against dismissal during his period of incapacity for work, and may therefore be dismissed.
Similarly, if the employee has informed his employer on the 1st day of his absence, but fails to send him the medical certificate within 3 days, he will no longer be protected beyond those 3 days.
Moreover, the lack of reporting on the 1st day of absence and/or the failure to deliver a medical certificate within the prescribed time limit may, depending on the circumstances of the employee, notably his seniority and whether or not there have been previous warnings, constitute an offence of negligence on the part of the employee, allowing in certain cases dismissal with notice.
Nota Bene
Also, unjustified absence of the employee may give rise, depending on the circumstances, to dismissal with immediate effect for serious misconduct.