Most physicians I now are comfortable letting someone else handle all the daily decisons that come up. They prefer to stay in a coccon and deny any responsibility for knowing where the paperclips are. While this is certainly less stressful than adding manager to their title, there are a hosts of problems that occur when a business relies so heavily on an individual employee.
Twice I have seen situations where a manager of some sort was embezzling funds from the business. If you empower an employee with what amounts to partnership status, don't be supprised when they act like a partner. This is not to say that you can't trust your staff. In fact, if you don't trust your staff you're in a lot more trouble than anything we can fix here.
If your Manager/Director/Whatever is the only one in your office/clinic who can run the place. Bite the bullet and make the change now. Businesses that are successful run on systems, not on individuals.