Dear Speechless: It’s a good thing you’ve put off confronting him, because it sounds as if you don’t have quite enough information yet. “Asking Joe directly what his problem is, at this stage, is not likely to get you an honest answer,” says William Dann, head of training and coaching firm Professional Growth Systems and author of a new book, Creating High Performers: 7 Questions to Ask Your Direct Reports. “To really understand what’s going on here, you need to go through a diagnostic process first.”

It may well be that at least part of the reason Joe’s work has been slipping is that he resents having been passed over for your job, says Dann, “but don’t assume that. First, you need to gather objective proof that his performance has declined.” Those old performance reviews you looked up may not help much, since “evaluations are notoriously unreliable. He may have had glowing reviews that meant nothing.” Ideally, you could find out what metrics former bosses used in arriving at those rave reviews, and compare those standards with your own. The differences, assuming there are some, could be important. “New bosses often assume that employees know what they expect,” Dann notes. “But usually, they don’t.”

Once you have strong evidence that Joe’s work has been slipping since you showed up — and of course, those blown deadlines and other errors you mention certainly count — don’t make his screw-ups the focus of the conversation. Instead, mention them briefly, then move on. “Say that you see your job as helping everyone on the team do their best work,” Dann advises. “If anyone’s performance isn’t first-rate, you want to understand why.”

Honest conversations between bosses and employees can be tough, he points out, simply because most of us are out of practice. “Any team is a partnership. The only way it works is if people are honest with each other,” Dann says. “Unfortunately, most people have never had an honest dialogue with their supervisor in their entire lives, or vice versa, so they don’t even know where to start.”

To make these potentially difficult conversations easier, over the course of his long career as a health care executive, Dann developed a list of seven questions he recommends that leaders ask every team member — starting, in your case, with Joe.

Do you understand what performance is expected in your job?

Do you know what good, or great, performance looks like in your job?

Do you get enough feedback on the results you produce?

Do you have enough authority to carry out what you need to do?

In areas where you don’t have authority, are you getting timely decisions from other people?

Do you have the data, resources, and support to do everything that’s expected of you?

Do you get credit for the results you produce?

Creating High Performers (which by the way, at just 117 pages, is admirably succinct and down-to-earth) goes into some detail about why each of these questions matters, and why it’s particularly important to separate them from any discussion about pay. But for your purposes, asking Joe — and the rest of your team — to answer them may turn up some answers that surprise you.

Let’s suppose, though, that Joe’s responses don’t give you any clear idea of what’s bugging him, or how to fix it. “It’s also possible that he’s having some kind of personal problem, and you can ask about that, with an eye toward trying to accommodate it if necessary,” notes Dann.

But, after ruling out everything else, you may well be left with what you suspect is the issue: You. “In that case, put all your cards on the table,” Dann suggests. “Say something like, ‘I can’t help thinking you’re angry because you didn’t get promoted to my job, and frankly, I don’t blame you. I’d probably feel the same way in your shoes. What can we can do to get past it?’”

What happens next is up to Joe. Dann warns in Creating High Performers that “I’ve seen entire organizations wrapped around the axle” by team members who drag their feet even after their bosses have made every reasonable effort to help. Here’s hoping that doesn’t happen here but, if it does, both you and Joe might well be better off if his current job search pans out.

Talkback: Have you ever had a direct report who suddenly stopped doing his or her best work? What did you do about it? Leave a comment below.