Haruki's Boss, Gabriel, Tells Him That Because He Has Been

Haruki's boss, Gabriel, tells him that because he has been such a valuable employee, he will receive an extra week of vacation. When Haruki decides to schedule the vacation, he reminds Gabriel of his statement. Gabriel says that he has changed his mind and that he really cannot afford to let Haruki have an extra week off. Haruki says that Gabriel has breached the contract he had with him for an extra vacation week. Assuming injustice cannot be established, who is right? Does a valid contract for an extra vacation week exist?