Can a teacher who makes a negative performance review against the teacher also sue the teacher for defamation?

In McIntyre v. Connolly (2008) CanLII 12496, the plaintiff’s employment was terminated and he grieved his dismissal under the collective agreement. At the same time, the plaintiff commenced a civil action for defamation. There was a settlement of the grievance and the employer filed a grievance alleging that the plaintiff failed to implement the settlement. The motion judge held that arbitrator had ruled that the parties had entered into a settlement which determined their rights, and that claims of defamation by a teacher relating to negative performance reviews or problems in the workplace are properly matters falling within the collective agreement. In the case at bar, the essential character of the dispute is not a problem in the workplace.