Section 60F of the Employment Act below may be able to give you some guideline especially (b). Another thing you can do is to complain to the Labour Department about your problem.
60F. Sick leave.
(1) An employee shall, after examination at the expense of the employer:
(a) by a registered medical practitioner duly appointed by the employer; or
(b) if no such medical practitioner is appointed or, if having regard to the nature or circumstances of the illness, the services of the medical practitioner so appointed are not obtainable within a reasonable time or distance, by any other registered medical practitioner or by a medical officer;