Yes, you can file defamation case against him for the whatsapp messages. You will need evidence and witness to bring before the Court such as the messages should be in your mobile and the other two persons who received the messages can be your witness. You can file a defamation case against the person for harm to your reputation, which is the only negative consequence that can arise from the act of defamation.
Section 499 of the Indian Penal Code covers defamation and states that any person who by spoken or written words, signs or visible gestures creates or publishes any imputation on any person with an intention to harm the reputation of that person is said to defame that person. The person making such imputation should have the knowledge or a reason to believe that such imputation will ruin the reputation of the person.
You will have to prove that real damage or harm has occurred to your reputation and your professional career. Section 500 of the Indian Penal Code states the punishment for defamation as whoever defames another shall be punished with simple imprisonment for a term which may extend to two years, or with fine, or with both.