Two teams from the English Premier League, Liverpool and Tottenham Hotspur, will feature in Saturday's 2019 Champions League final. After felling giants like Lionel Messi’s Barcelona and English superpower Manchester City, both teams have the opportunity to bring home the glittering, crown jewel of European soccer.

While this season’s journey to Madrid’s Wanda Metropolitano Stadium has been most notable for, as Ed Caesar wrote in the New Yorker, its “nerve jangling theatre” and improbable comebacks, it has also been marred by reminders of the game’s physical consequences.

These examples illustrate, among other things, the potential holes in current soccer concussion protocols.

Liverpool talisman Mohamed Salah suffered a concussion in a harrowing head-to-player collision only days before the second leg of the Champions League semi-final against Barcelona. Though Salah sat out the Barcelona game, he returned the following weekend to buoy Liverpool’s Premier League title aspirations in a win against Wolverhampton.

And yet, just a few days before Salah went down, Tottenham defender Jan Vertonghen was deemed fit to play only minutes after a bloody collision with Ajax’s Toby Alderweireld in their Champions League semi-final clash. But soon after play resumed, Vertonghen left the field after he struggled to stand. (Tottenham released a statement saying Vertonghen did not suffer a concussion as a result of the collision.)

These examples illustrate, among other things, the potential holes in current soccer concussion protocols. The proper assessment and treatment of concussive, and even subconcussive, hits grows increasingly important as fears grow about soccer players developing degenerative brain diseases like chronic traumatic encephalopathy (CTE). CTE is still mostly associated with the NFL, but it is hardly exclusive to American football.

The human brain floats like a balloon inside of the skull. When the head is hit, the brain bounces back and forth, twisting and/or stretching within the skull. This rapid motion results in the traumatic brain injury known as a concussion.

And as a cascade of changes occur at the cellular and chemical levels of the brain, neurologic havoc results in the body. It can leave a concussed footballer with short and long-term effects.

This was how current ESPN soccer analyst Taylor Twellman’s career prematurely ended. Once one of Major League Soccer’s most successful goal scorers, Twellman was punched in the face during a collision in 2008. The residual effects from this concussion limited his games in 2009 and eventually forced him to retire in 2010. Given the silence on the issue of traumatic brain injuries in soccer, he began a foundation to advocate for the cause.

Twellman is among a growing chorus of critics who have accused FIFA, the governing body of association soccer, of not taking concussions seriously. And while the world’s leagues (English Premier League, Spain’s La Liga, Germany’s Bundesliga, etc.) may fall under separate umbrellas, all the leagues broadly follow similar guidelines.

Twellman is among a growing chorus of critics who have accused FIFA, the governing body of association soccer, of not taking concussions seriously.

In the 2014 Men’s World Cup, a concussed German player, Christoph Kramer, had no recollection of the game after he continued to play for 15 minutes after a brutal collision. In 2015, more deficiencies in the concussion protocol were highlighted after the mishandling of a collision involving the United States’ Morgan Brian in the Women’s World Cup semi-final.

Prior to the 2018 Men’s World Cup, FIFA responded to the furor by instituting a new rule that allowed referees to stop play for up to three minutes and permitted medical teams time to evaluate a player with a suspected concussion. Another rule change granted team doctors the final say on whether a player was suitable to remain in the game after a physical assessment and use of in-match video replays of the injury. While FIFA suggest a concussed player wait at least six days before playing again, it has no way to force teams to do so.

These reforms, however, are not enough. While concussions can be hard to evaluate, experts state a reliable diagnosis requires a neurologic exam that takes roughly 10 minutes. And while team physicians should get the last word on an injured player’s ability to return to the field, they are not protected from managers who may be motivated to keep a player in the game at all costs. Unsurprisingly, Premier League doctors have recently voiced concern about manager influence in concussion cases.

These deficiencies were highlighted in the 2018 Men’s World Cup when an obviously concussed Moroccan player, Nordin Amrabat, was repeatedly slapped in the face by team medical staff in an effort to wake him up.

But FIFA has also failed to develop an effective way to identify players with suspected head injury. A 2018 study published in JAMA Neurology reviewed video from the 2018 World Cup and found that more than 63 percent of players who showed two or more concussion symptoms failed to get evaluated by a licensed clinician. This was a slight uptick from 2014, when the figure was almost 57 percent.

As these players continue to play, the risk mounts. Ajay Premkumar, the study’s lead author and an orthopedic surgeon at New York's Hospital for Special Surgery, noted, “Playing with a concussion increases the athlete's risk for more severe traumatic brain injury or 'Second Impact Syndrome,' which can have devastating complications.” He added that there is “significant literature which supports increased symptom severity and a longer recovery time for those who continue to play after a concussion compared to those removed from gameplay."

None of this takes into account what happens when players head a soccer ball, an action that does not result in obvious neurological symptoms but can still injure the brain.

None of this takes into account what happens when players head a soccer ball, an action that does not result in obvious neurological symptoms or often cause concussions but can still injure the brain. In addition to head-ball drills in practice, an average player can collide with the ball 6 to 12 times per game — at least 2,000 times over a 20-year career.

This impact is not benign. A Purdue University study on women’s soccer concluded that the force generated by heading a strongly hit ball was similar to getting tackled in American football. While men have stronger necks that can better absorb the blows, the quantitative forces generated in a Champions League collision today may be even greater.

Eric A. Nauman, a professor of mechanical engineering at Purdue, observed, “If you actually compare the brains of people who have taken lots of sub-concussive hits to ones that have taken a single big hit, the sub-concussive brains often look worse. I don’t think people appreciate that yet.”

But while CTE’s frightening prevalence in NFL players has had a tectonic effect on the sport, attention is starting to shift to soccer. A 2017 study in Acta Neuropathol on dementia in retired soccer players found pathologic evidence of CTE in four of six post-mortem brain examinations.

And while CTE has been classically attributed to concussions, a 2018 study in Brain concluded that subconcussive, repetitive hits (for example, heading the ball) can also cause the condition. This may be consistent with the case of Jeff Astle, an English footballer whose early death was found to be related to brain trauma suffered from heading the ball repeatedly.

FIFA and other governing bodies need to embrace the urgency of this issue. To start, independent neurologists should be tasked with making the final judgment on a player’s fate, a 10 minute “concussion substitute” should be implemented to allow doctors sufficient time to examine a player thoroughly on the sidelines and a more thorough examination of heading should be undertaken. A handheld saliva monitor to detect surrogate biomarkers for brain injury may be available within two years.

While the threat of injury is perpetual, the risks can be minimized. We need to better understand and manage concussions if we want to make sure the talents of players like Mohamed Salah and Jan Vertonghen are preserved.