Legal Question in Employment Law in New York

It does not sound like it. In order to be defamatory (libel or slander), the statement must be asserted as a statement of fact (not of opinion), it must be false, it must be published to a third party, and there must be quantifiable damages. Here, the exact words used are important for discerning whether the statement was asserted as fact or opinion. If the employee said, "I think he or she will be fired", that is opinion, not fact and not actionable. Secondly, there do not appear to be any quantifiable damages. There is a class of defamation where damages are presumed (slander per se), where somebody is impugned in their occupation or profession, but this would not seem to apply since the employee did not say you were incompetent or unable to perform the functions of your job, but merely that you were being fired which can typically mean with or without cause. Please note that more information is required to give the most appropriate legal opinion.