It is sick leave if the worker does not agree. But the will be no replacement. In the proviso below, note the words "...shall not apply during .....or on sick leave..."
"59 Rest day
Provided that this subsection shall not apply during the period in which the employee is on maternity leave as provided under section 37, or on sick leave as provided under section 60F, or during the period of temporary disablement under the Workmen's Compensation Act, 1952, or under the Employees Social Security Act, 1969. "