The 2 reporting obligations (described in the foregoing question) are also applicable in the event of prolongation of the illness.
Examples
The employee has a medical certificate from Monday 7 to Friday 11 May 2018 inclusive.
In the event of extension of the absence on account of sickness, the employee must give notice to his employer no later than the 1st day of expected resumption of work (Monday 14 May 2018) and must submit the medical certificate within 3 days (no later than Wednesday 16 May).