Maybe the most interesting free-agent case of this coming summer — and perhaps the most interesting in recent memory — will be that of sunken star guard Isaiah Thomas. We’ve seen free agents take nosedives just ahead of what looks like a big payday in the past. But we’ve never quite seen what’s happened to Thomas in the past 12 months.

He didn’t get arrested. He didn’t get suspended on some drug violation. He didn’t hurtle himself into the stands to go after heckling fans. He didn’t kick a cameraman on the sideline. We’ve seen all that before.

Thomas has dropped in free-agent stature almost through no fault of his own. The problem here is his hip, which front-office execs around the league fear is either pre-arthritic or already arthritic. Maybe the only way that Thomas has hurt his own free agency has been by not choosing to have hip surgery sooner during last season, when he was an All-Star and an MVP candidate for the Celtics.

"It’s a red flag that he did not have surgery on it," one general manager told Sporting News. "If you have a problem that can be fixed heading into your free-agent year, you get surgery. If there is concern that you can’t fix it with surgery, that means probably there is something more wrong. It is something that, obviously, the doctors will look at closely."

Thus, Thomas went from a max-contract candidate (remember, he said that Celtics president Danny Ainge would have to bring a "Brinks truck" to re-sign him) to a guy who will have to wait out the first wave of free agency this summer and hope to get picked up on a decent, short-term deal to rebuild his stock.

Thomas, after averaging 28.9 points for Boston last season and establishing himself as the league’s top fourth-quarter producer, missed the first two-plus months of this season, played for about a month in Cleveland and another month after being unloaded to the Lakers, combining to average 15.2 points in 32 games, shooting 38.3 percent from the field and 29.3 percent from the 3-point line.

"Just given the way he played last year," another NBA executive said, "I think you can’t go more than one year on him. Maybe you can do two years if you hold the second year at your option. That’s before you even get into whether he is healthy."

Let’s dig in there, because the notion that Thomas’ hip is not completely healthy — something most front offices seem to take as gospel — contradicts what Thomas himself said earlier this month. According to Bill Oram of the Orange County Register, Thomas said, "Now the problem is fixed and (I’m on) the road back to 100 percent."

Fixed is likely an overstatement, if speculation that Thomas is pre-arthritic or already has arthritis in the hip is true.

As we ought to do in these situations — a degree in journalism does not give this humble sportswriter the authority to explain the finer aspects of hip maintenance and repair — we turn to an expert, Dr. Derek Ochiai, a sports medicine orthopedic surgeon and hip specialist for the renowned Nirschl Orthopaedic Center in Virginia.

Dr. Ochiai is careful to point out he has not seen Thomas’ hip and has no special knowledge of his case. But the way that Thomas said he was "fixed" would cause hip surgeons everywhere to raise their eyebrows.

"If there was some early gliding cartilage damage, you can’t fix that," Dr. Ochiai said. "You can’t make it normal. You can help it. He said he is fixed after his surgery. He is fixed either meaning he didn’t have any gliding cartilage damage and he is fine, or he does and he is saying fixed, as in he is better than he was.

"But that’s not the same as not having any cartilage damage in his hip."

OK, that’s an orthopedist speaking. Dr. Ochiai was nice enough to explain what he means for us laypeople.

There are two types of cartilage on the hip. There is the labrum, which is on the hip socket and cushions the ball of the femur that fits into the socket. There is also the gliding cartilage, which is the cartilage that covers both the ball of the femur and the socket itself, ensuring there is no bone-on-bone contact.

Typically, a hip problem starts with an impingement, which is some minor misshapen element of the ball of the femur. That usually begins when a patient is in his or her teens. Over time, the impingement in the bone rubs against the hip labrum and causes it to tear. A torn labrum in a hip can be fixed, usually with a surgery of about three or four hours and three-to-six months of rehab.

It gets dicey when the question becomes just how long the impingement has been tearing at the labrum, and what effect that has on the other cartilage. There’s no set time — sometimes it happens quickly, sometimes over many years — but the torn labrum can lead to the wearing away of the "gliding cartilage" that Dr. Ochiai mentioned. Again, that’s the cartilage on the top of the femur and in the hip socket that prevents the bone from rubbing together.

Once the gliding cartilage is damaged, as Dr. Oihcai said, it can’t be fixed (except, maybe, with a microfracture procedure, which most athletes try to avoid these days). Arthritis is likely the next step, and at that point, all a patient really can do is manage pain.

League officials worry that the reason Thomas did not have hip surgery earlier — why he chose to attempt rehab after the 2017 season — was that he already had signs of gliding cartilage damage. That makes some sense to Dr. Ochiai.

"There are different reasons for choosing rehab over surgery," Dr. Ochiai said. "A lot of times if you have a labral tear, it has been around for a while. It didn’t just happen overnight, and the pain can gradually increase. They might know you have a labral tear and just try to work around it with rehab.

"But arthritis is an increased risk, and by the time someone makes the decision that, ‘This is too painful and I need to have something done,’ they might already have early arthritis. And if you have early arthritis, the chances of a successful hip arthroscopy go down. So you try the rehab. But if the gliding cartilage is OK, you’d usually pick the surgery."

All this is not to say that Thomas can’t return to being a productive NBA player. He is a 5-9 All-Star, after all, a guy who was the last pick in the 2011 draft and became a star despite being discarded by the Kings and Suns, of all teams. He’s beaten some odds in the past, and maybe damage to some gliding cartilage in his hip won’t be enough to keep him from a full comeback.

If Thomas has to play with an arthritic hip, on the floor, he could find he has a reduced range of motion with his leg, that his first step is slightly slower than it’s been, that he is less explosive when jumping.

Off the floor, he would be subject to more swelling and increased pain. Of course, he’s gotten accustomed to hip pain in recent years. But any team that signs him this summer will protect itself against the possibility that Thomas has serious hip damage.

"I think everybody likes the guy," the GM said. "You root for him. But do you want to pay him $12 or 14 million when you know you’re also paying for all the headaches that his health could give you? Someone will get him, but it’s going to be a low-risk deal."