In January 2016, Kansas City Chiefs lineman Laurent Duvernay-Tardif suffered a concussion in the first half of a playoff game against the Houston Texans. There were 271 concussions in the league that season, but Duvernay-Tardif, who was also attending medical school at McGill University during the offseason, understood the implications as well as any football player who’s ever suffered a head injury has. “Concussions is one of my fields of interests,” he told me last summer. “I’ve read a lot about it. Especially when you study pediatrics, which I do, because it’s one of the biggest injuries for kids under 16.”

Duvernay-Tardif recognized the symptoms as soon as he began to display them: “I’m the one who went to the trainer and said, ‘Something is wrong.’ And the reason I was able to do that was I had knowledge.”

While waiting to get cleared for game action the following week, Duvernay-Tardif dove further into his research, reading additional studies on the prognosis for concussions, including examining the testing and “scoring system” that he’d have to go through to prove health and return to the field. He’s now in his medical residency. He’s also still starting for the Chiefs, and I can’t think of a clearer example of how complex the NFL’s concussion issue is than that: Despite all of his knowledge, and despite his personal battle with a concussion, Duvernay-Tardif still plays.

On Tuesday, the concussion conversation acquired a new and more urgent dynamic: Boston University researchers say that they have developed a way to test living patients for CTE, a neurodegenerative disease whose symptoms can include confusion, headaches, memory loss, depression, and impaired judgment, and that has been heavily linked to football.

Concussions were already scary, even though the media tend to downplay the problem. A study from earlier this year found that journalists often soften the tone of the injury when relaying information to the public. We too often think of concussions as a problem for a coach trying to assemble a game plan absent a key player, and not as a life-changing event for that player. But Bears linebacker Leonard Floyd said he did not think straight for two months after his concussion; Aaron Rodgers once told Bill Simmons that one of his eyes went “metallic” after a concussion.

“I think about how we’re almost numb to it because it's a part of the job,” then-Lions linebacker DeAndre Levy wrote on Instagram last year. “I became numb to the fact that CTE could be present in me.” If a test exists that reveals that presence to players, it will change the conversation around head injuries. And it will change football.

In most of the conversations about head injuries and football that I’ve had with people knowledgeable about the subjects, there’s always been a far-away if inserted: If one day, CTE could be diagnosed in the living, the way we view football would change. In the decade or so since head injuries became a focal point of football conversation, CTE has seemed less urgent to the casual fan on Sundays because it previously could only be diagnosed in the deceased. While the BU researchers have cautioned that their findings are still in the early stages, the implications are already considerable. No sport commands as many viewers as the NFL, and no sport can retain as many sponsors and navigate as many crises. But the ability to test for CTE at any point during a player’s career—including long before he ever reaches the NFL—could send the sport spiraling.

If football fades in popularity, it won’t primarily be because of fans who are fed up with the ethical issues surrounding the game—be it health and safety, criminal behavior, or boycotts. Despite the amount of attention on those issues, they haven’t specifically caused any ratings declines. In fact, in the decade-plus since we first came to understand the sport’s lingering impact on a player’s body, football has become more popular.

There will always be some level of cynicism about health and safety in football, both inside and outside of the game. ESPN’s Darren Rovell said that the NFL players he’s spoken to don’t care to know if they have CTE since it’s already a virtual certainty. This is a sport in which Jets rookie Jamal Adams said he’d like to die on a football field. But Tuesday’s news is not just about what current players say about the sport, because testing is still in its early stages of development. This is about future players one day knowing at an early age—perhaps before their NFL careers begin—that they have a brain disease. What if colleges decide to test for CTE for liability purposes before players’ careers begin? If large numbers of players are diagnosed with CTE during their college football days (where the numbers suggest there’s already a problem), what will the fallout be? Will colleges prevent them from playing again for liability or ethical reasons? Will young people get discouraged from ever starting the sport? Participation in the sport is already down in youth football since the start of this decade. The ability to decipher when CTE begins will be a massive win for player safety—and a massive problem for the viability of the game.

If the NFL’s reach wanes, it will almost certainly be because the talent pipeline drains. Armed with the information that BU’s breakthrough could one day give to them, the players who stay in the game long enough to become stars in the NFL could end up bailing midcareer, especially after they’ve made a nice amount of money. NFL fans watch nationally televised games because of gambling and fantasy, yes, but history suggests they also watch for superstars. But let’s say you are a 30-year-old NFL superstar fresh off a four-year mega-contract. You take the test and you find out that you already have CTE and that it could get even worse if you continue to take repeated blows to the head. You know that studies have linked longer careers to more severe cases of CTE. What do you do?

Only a few players have quit with health specifically in mind: Former Chiefs safety Husain Abdullah and 49ers linebacker Chris Borland are among them. Ravens lineman John Urschel retired in July, which a team source told ESPN was in part because of a study released days before that said that CTE was present in nearly 99 percent of the brains of deceased NFL players that were studied. Those are not the names that necessarily impact the ratings and watchability of a league already facing questions about those things. But if the league lost a wave of superstars to either midcareer retirement or never making it to the pros in the first place, the game would fundamentally change. That reality becomes much more realistic once science is able to tell a player in the middle of his football life how much damage his brain has already taken.

There is no law that says football has to be the most popular sport in America. It is well-worn ground to point out that boxing used to be significantly more popular than it is today, but it’s a point worth thinking about nonetheless because it reminds us that once the talent pool in a given realm goes away, the popularity of the game soon follows. “The same world-class athletes that once gravitated to boxing—strong guys with superior hand-eye coordination, lower-class backgrounds, looking for a way out,” Simmons wrote in a 2002 love letter to boxing’s bygone era, “now gravitate toward basketball, baseball and football (where top stars earn more money and escape with their brains intact).” Boxing certainly has other problems—the lack of a unified governing body, off-the-wall scoring decisions—but if there were a critical mass of high-caliber heavyweights battling right now, viewers would be more engaged.

We’re still years away from the NFL needing to contend directly with talent drain. But the only way to keep as many players coming into the league is to make the game as safe as possible, something that the NFL is at least attempting to do. I’ve spoken to many of its health and safety experts, and they are trying new technology and implementing medical advancements both to attempt to prevent concussions from happening (through things like new helmet technology) and to treat them once they occur (with improved testing and independent neurologists who can give an unbiased assessment of when players can return to the field). It is, as of yet, unclear what impact these efforts will have on the sport. And of course, the inherent problem remains: Hitting one’s head is always going to be dangerous. Flag football may be on the rise, college football may be reducing contact in practice, and the Canadian Football League may be getting rid of full-contact practices entirely, but nothing can change the reality that playing a game that requires repeatedly pounding one’s head against another human will eventually cause problems.

What’s more: If CTE is diagnosed in the living, the ramifications for the NFL would also extend beyond the field of play to the courtroom. As former Packers executive and current MMQB columnist Andrew Brandt pointed out, CTE still isn’t a covered condition in the NFL’s concussion settlement, which was struck in 2013 and approved in 2015, and in which the NFL agreed to pay about $765 million to ex-players—an amount that has since jumped to around $1 billion. (Because CTE could never be proved in living people before, the settlement covers diseases stemming from CTE, such as dementia, but not CTE itself.) But if players file motions against the NFL, armed with the information that CTE could be diagnosed in the living, it would add a new layer to the concussion settlement. In fact, former NFL player Seth Joyner suggested just that, calling the news a “game changer.” Once it’s possible to confirm, nearly in real time, that CTE exists, there will be liability issues everywhere. Could a college be sued? Could a high school?

At the beginning of his 1982 book, The Hardest Game, Hugh McIlvanney wrote an essay about the ethical ramifications of enjoying boxing. “Any supporter of boxing who does not admit to some residual ambivalence about its values, who has not wondered in its crueller moments if it is worth the candle, must be suspect,” he wrote. In order to survive, football must be thought of by fans and players alike as a game that people should play. The sport is losing that battle at the moment, and if Tuesday’s news leads to the clarity that it seems to promise, that outcome will only be more assured.

Football has always been a violent game. Its legends of yesteryear often regret playing the sport, with Bo Jackson becoming the most recent superstar to voice that. A few years ago, Tom Brady’s father wondered aloud if he’d let his son play football if he were a kid in this era. Now that stands to become more of a mainstream opinion. It will take years to find out the true impact of Tuesday’s news, but it brings us closer to understanding what’s happening to these players before it’s too late.