Expressions of opinion are not defamatory; to be defamatory the statement must be untrue and an opinion cannot be. As it stands, if this statement is made in isolation is probably an opinion. If you proceeded to enumerate the reasons why you hold this opinion, then it starts to move more towards a statement of truth or untruth.

Of course, if the court was convinced that they were, in fact, unprofessional and lacking in integrity, then that is not defamation either.

Also, defamation requires making an untrue, derogatory statement to a third-party. Telling someone they are a no good thief with the morals of an alley-cat is not defamatory; telling someone else is.