In respect of employees covered under ESI, the employer is making his contribution to the ESI and as such the employee cannot say that he had consulted private physician and his medical certificate should be taken as supporting document but he is expected to produce medical certificate from ESI only. If the company has a medical officer, obviously, the certificate from that medical officer can only be taken as valid certificate. In exceptional cases, where the employee was on leave (other than medical leave) and was out of station and during the leave period he fell sick and wanted to avail extension of leave on medical ground, and for that he can use the medical certificate of private doctor as a supporting document. Very simply, in respect of ESI covered employees medical certificate from a private medical officer can be used as a supporting document but not as proof of medical or sick leave.