A few years ago Sir Alex Ferguson accused David Luiz of “rolling about like a dying swan” to get one of his players sent off. But the Chelsea defender clearly wasn’t hamming it up at Bournemouth last week when a Josh King piledriver nearly took his head off. As Luiz toppled to the ground, TV commentators suggested he had been “absolutely poleaxed” and “kayoed”. Yet, incredibly, after a quick once-over he was back in action. As the NFL player JJ Watt dryly noted: “Knocked out cold, then back playing like a champ 45 seconds later. I guess the concussion protocols are a bit different across the pond.”

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And elsewhere, too. Last month the UAE defender Fares Juma Al Saadi was knocked out after a sickening clash of heads with Australia’s Mathew Leckie in an Asian Cup quarter-final. It was so bad that Juma left the pitch on a stretcher with his neck in a brace. Yet, miraculously, a few minutes later with the UAE 1-0 up in added time, he groggily returned. Four days later he was back for the UAE’s semi-final against Qatar – a decision that led the players’ union, Fifpro, to question publicly whether Fifa’s return to play protocol was followed.

They were not the only ones with concerns. When I spoke to Dr Eric Nauman, who studies the impact of collisions on the brain in high school soccer and American football players, he was flabbergasted that both men had returned so quickly. As he pointed out, the symptoms of head injuries can take time to develop. “And with all the other research out there, it should be patently obvious not to put somebody right back in like that,” he added.

Juma’s case was even more worrying, said Nauman, because of the dangers of second-impact syndrome – which occurs when the brain swells rapidly after a person suffers a second concussion before symptoms from an earlier one have subsided, risking long-term damage. “It looked like Juma took two impacts almost simultaneously and one was head-to-head,” he pointed out. “The fact he was knocked out puts him at serious risk, especially if the brain gets hit again – even if it is just from heading a goal kick or a keeper’s punt.”

Facebook Twitter Pinterest Mathew Leckie of Australia and Fares Juma Al Saadi of United Arab Emirates receive treatment in their Asian Cup match. Photograph: François Nel/Getty Images

Both incidents reinforced something we already knew: when it comes to head injuries football’s rules are not fit for purpose. As things stand, doctors have three minutes to assess a concussion, far less than the 10 needed to do a thorough head injury assessment. And yet a fix would be frustratingly easy to implement – all the game would have to do is allow replacement substitutes for suspected concussion cases, as in rugby union. However, last year the chairman of Fifa’s medical committee, Michel D’Hooghe, came out against it, fearing that teams might exploit it for tactical reasons. Perhaps they would. Yet better that, surely, than incentivising players to put team success over their own health?

Some might believe we should trust athletes to know enough about concussion these days to understand when they are OK to play on. New research, however, does not bear this out. A study published in December, based on interviews with 257 professional boxers, mixed martial artists and martial artists in Nevada, found that only 43% said they understood the symptoms of concussion either ‘very well’ or ‘extremely well’. Meanwhile 63% admitted their knowledge of the long-term effects of multiple concussions was non-existent, scant or basic – a worryingly high number given the dangers of CTE, the brain condition associated with repeated blows to the head, are increasingly well known.

More alarmingly the research, published in the Physician and Sportsmedicine, also found that around 40% of fighters reported returning to training or competition the same day they felt a concussion was sustained. Why? The main reasons given were a love of fighting, their career aspirations and a desire to win – a jumble of factors that might sound coherent in the heat of battle, but rather less so when long-term brain damage kicks in.

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Such blase attitudes are not uncommon. A study of 829 retired NFL players, published in the American Journal of Sports Medicine last year, found that just over 50% did not inform medical staff of a sports-related concussion during their professional careers. Other studies suggest that at high school (57.2%) and collegiate levels (68.2%) the nondisclosure prevalence among American football players is even higher. It doesn’t matter what the sport is: too many players still keep schtum when it comes to head injuries for fear of being taken off the pitch, or being seen as weak.

Clearly part of the answer is for better regulation and education. As the researchers in the fighter study point out, those involved in boxing, MMA and martial arts need to find a way of encouraging athletes to self-report concussions. One way would be to point to research showing that concussed athletes who carry on playing or fighting take longer to recover.

In the longer term, science is likely to provide better diagnostic tools. Clearly it is not practical to have MRI scans on the side of the pitch. However, Nauman tells me that one of his collaborators at Purdue University, Yunjie Tong, is working with a pitchside system, fNIRS, that measures brain blood flow and takes about 10-20 minutes to work. True, that will feel like an eternity if you are David Luiz or Juma, itching to get back on. But better certainty than calamity.