Virginia is an at will state and you can be fired for any reason that is not specifically prohibited by law. The reason here is not one of those reasons. Now for defamation, you must prove that the statements were false, were communicated to another party, and that those statements caused damage. This is a difficult burden to meet. In this case, you also have to prove that the prior employer told the prospective employer something that fits into the definition of defamation.
[I am a Virginia-licensed attorney. This communication is intended as general information and not specific legal advice, and this communication does not create an attorney-client relationship.]
Sign up to receive a 3-part series of useful information and advice about personal injury law.