If an employee claims to be ill or injured,no fault of his employment,and tells his manager that he needs to sit down at work,but has no doctors note or medical records to back up his injury,does the employer have to let the employee sit while workin

If an employee claims to be ill or injured,no fault of his employment,and tells his manager that he needs to sit down at work,but has no doctors note or medical records to back up his injury,does the employer have to let the employee sit while working? 98% of the employees in this department stand and it is an inconvience to the company to let one person sit all the time. Also if they allow this employee to sit without a doctors recommendation,doesn't any one who claims they need to sit down because of injury have to be allowed to sit.