In one of the judgments, the Supreme Court of India has observed: 

“(3) A professional may be held liable for negligence on one of the two findings: Either he was not possessed of the requisite skill which he professed to have possessed, or, he did not exercise, with reasonable competence in the given case, the skill which he did possess. The standard to be applied for judging, whether the person changed has been negligent or not, would be that of an ordinary competent person exercising ordinary skill in that profession. It is not possible for every professional to possess the highest level of expertise in that branch which he practices.” 

Reference

1. 334 / 2005 / SCI / 144-145 of 2004: Jacob Mathew vs State of Punjab and Anr: 5th day of August 2005: R C Lahoti, CJI: Hon’ble Mr. justice G P Mathur, Hon’ble Mr. P K Balasubramanyan.