Wife Concerned About Husband's Private Meeting with Female Boss

How should my husband relate to his female boss? Occasionally, she needs to discuss a business matter with him that requires privacy and so she will schedule a lunch appointment with him alone. I'm uncomfortable with this, but he sees no alternative since this kind of practice is common and expected in his line of work. In fact, to raise this as a concern would make things difficult for him professionally. What are your thoughts and what should he do?