(CNN) More than 3 billion people around the world tuned in to watch soccer's 2014 FIFA World Cup, during which there were 81 head collisions. And only 15% of those injured players received a concussion assessment from health care personnel, according to a report published Tuesday in JAMA.

"I was hoping to find that people would be properly assessed for potential concussions, just like if they were injured in their ankle or their knee, that they would be properly assessed for that medical injury," said Dr. Michael D. Cusimano, a co-author of the study and a staff neurosurgeon at St. Michael's Hospital in Toronto.

He and four trained reviewers observed video footage of all 64 matches in the 2014 World Cup, soccer's prestigious international championship. They took a close look at players who exhibited two or more signs of concussion, such as head-clutching, being slow to get up, disorientation and seizure-like movements, according to the study.

Cusimano found that of the 67 occasions in which players exhibited two or more signs of a concussion (of the 81 total head collisions during the matches), 79% returned to play. Only three of the affected players were removed from the match.

"There's a laissez-faire attitude about our brain," Cusimano said. "If they suffer a brain injury, there's still a tremendous lack of awareness. There's still a tremendous stigma about the player reporting their symptoms, never mind seeking help. It's kind of an invisible injury, and I think FIFA has a challenge and an opportunity here that they can step up and meet."

FIFA, international soccer's governing body, said in a statement in response to the new study that it "regularly monitors the situation of head injuries, maintaining constant contact with current and on-going studies on this matter and reviewing our protocols. Please note that following a series of cases at the 2014 FIFA World Cup, FIFA introduced in September 2014 a new head injury protocol to be applied to all FIFA competitions."

Under the protocol, a referee has the ability to stop the game for three minutes after a suspected incident of concussion occurs, allowing time for a team doctor to complete an on-site assessment. The referee can only allow the player to return to the game with authorization from the doctor, who makes the final decision.

In February, an unrelated study said that four former soccer players with advanced dementia were also found to have chronic traumatic encephalopathy, commonly known as CTE. This neurodegenerative disease is found in people who have suffered repeated blows to the head, which commonly occurs in contact sports.

Dr. Joseph E. Herrera, system chair of the Department of Rehabilitation Medicine at Mount Sinai Health System, who was not involved in the new report, is not surprised at its findings but thinks concussion assessment in sports has greatly improved over the past few years.

"Five or six years ago, before concussions became an issue, players would continue to play. Now, interestingly enough, we have players coming up to us and saying, 'Hey, doc, that play didn't look right. He may need to come out.' And that was unheard of a few years ago," Herrera said. "So the severity of concussion and to quell it moving forward has had heightened attention from coaches, players, trainers and physicians."

The new study includes a recommendation to implement health examiners, who would be independent of a team, in professional soccer matches. Herrera supports the idea, saying it would give medical examiners the opportunity to assess players objectively.

Youth sports are also facing issues, with a study in March showing an increase in concussions in boys and girls playing high school soccer between 2005 and 2014.

Adam Manning, vice president of communications for the developmental American Soccer League, said the move toward safer practices in soccer might take a while.

"I think that this is going to be very hard to change overnight, with a culture of coaches and players and people not knowing the data or not realizing how bad it can be," he said. "I've had numerous concussions, and I'm dealing with those side effects as a 35-year-old. So there's long-term effects that people will never know about unless they've actually experienced it for themselves."

Manning played soccer throughout high school and for one year in college, and he said he's had 11 concussions. Twice, he said, he was knocked out while playing and put back into the game after halftime. He still experiences short-term and long-term memory loss, headaches and extreme irritability, he said.

Join the conversation See the latest news and share your comments with CNN Health on Facebook and Twitter.

Cusimano said he believes the improper assessment of concussions seen at the sport's highest level could be a bad influence for lower levels of soccer.

He detailed the case of Christoph Kramer, a midfielder for Germany in the final against Argentina. After getting elbowed in the head, Kramer was assessed for 83 seconds and returned to the game immediately. In the minutes that followed, he exhibited signs of concussion and was unable to follow the plays. He was removed from the game 13 minutes after the initial collision.

"That's the wrong message that we're sending to all these other levels of play," he said. "If it happens at that level, when we have very clear recommendations from the top level of the American directorate at FIFA, then what are we saying to kids' soccer and collegiate soccer and all those levels in between?"