A new study by researchers in Toronto suggests that many of the world's top soccer players aren't being properly examined for possible concussions.

The results could have an impact around the globe since soccer is one of the world's most popular and fastest growing sports, said Dr. Michael Cusimano, senior author of the study published Thursday in the journal BMJ Open.

"What goes on at that elite level has huge effects all around the world and it may lead to undiagnosed concussions or improperly treated players, which could have significant consequences," said Cusimano, a neurosurgeon at St. Michael's Hospital in Toronto.

Researchers watched all 51 of games in the 2016 Euro Cup for the study, looking for moments when a player suffered a potential concussion due to a "direct head collision."

They watched for known signs of a concussion, including a player losing consciousness, being slow to get up, appearing disoriented or clutching their head. They also marked whether the player was medically assessed, as is required under internationally accepted guidelines for treating potential concussions.

The researchers identified 69 "potential concussive events" throughout the tournament and determined that in 19 events, or 27.5 per cent of the cases, players were examined.

But athletes were not checked out in the other 50 events, representing 72.5 per cent of all incidents flagged by the researchers.

In all 69 cases, players returned to the field before the end of the game.

Those results are concerning, Cusimano said.

"What goes on at these tournaments is watched by literally hundreds of millions of people so they can have a huge effect on how the sport is played and what happens when these events occur," he said. "So if (concussions) are ignored at this level, that same sort of style of assessment will carry on down to all the other levels of play."

When athletes experience a potential concussion, they need to be removed from play and examined by a qualified professional using a standardized test, Cusimano said. If they show signs of a concussion, they should not be allowed to return to the game.

These tests take a minimum of 10 minutes, he added, and conducting them on the side of the field isn't easy.

"You need time to properly assess a player. And imagine trying to do it on the sideline with 60,000 people screaming and yelling and noise and things going on. That is very, very difficult for a doctor or a professional trainer or anybody to do properly," he said.

Soccer's rules are one of the factors keeping potential concussions from being diagnosed, the study found, because the set number of substitutions and injury time can discourage a coach from pulling a player for medical assessment.

UEFA president Aleksander Ceferin said Wednesday that the organization wants doctors to have more time to assess head injuries so concussed players aren't put back onto the field.

He also said there could be a change to the rules on substitutes, but did not comment on whether that could mean temporary replacements for players with head injuries -- something world governing body FIFA has resisted.

"The health of players is of utmost importance and I strongly believe that the current regulations on concussion need updating to protect both the players and the doctors and to ensure appropriate diagnosis can be made without disadvantaging the teams affected," he said.

Changing rules is just part of addressing head injuries in soccer, said Cusimano.

Governing bodies also need to think about bringing in independent "spotters" who can look for signs of concussion without the pressure of being associated with a given team.

More education is also needed about the impact of head injuries, especially in countries outside of North America, he added.

Sports fans and sponsors also have roles to play.

"I think as long as sponsors are tolerating this kind of behaviour, I think they're sort of playing a part. They could stand up and say 'We don't agree that your referees aren't stopping the play,' " Cusimano said.

"There has to be a concerted effort from multiple levels. ... Money speaks very loudly."

Canadians and people around the world also need to think about changing our attitude towards sports to focus on healthy lifestyles instead of competition, Cusimano said.

"It boils down to what we do we tell kids right from the earliest age," he said. "What's more important -- to keep your health or to win?"

With files from The Associated Press. By Gemma Karstens-Smith in Vancouver