As long the MC is issued by licensed doctor then manager have to accept. What the manager could do is reward more to those "healthy" employees.

Some HR has a guideline stated if an employee taken more than 5 days MC in a financial year, 0.5 will be deducted from the overall performance rating.

When an employee is on MC, his/her colleagues need to cover the dept's commitment. So reward those work extra. Fair an square.