RIO DE JANEIRO (AP) -- Felled by an opponent's knee to the head as they both chased the ball, a player is seemingly out cold on a World Cup pitch. The clock is ticking. Millions are watching. National honor, careers and sponsorship dollars are at stake.
Groggily, the player wakes up and argues furiously with his team doctor that he must play on. For anyone attuned to the dangers of concussions and head injuries, this is when alarm bells ring - just as they did when this scenario unfolded at the World Cup in Brazil.
As in American football, team doctors should be able to pull a player off the field and calmly determine whether the player can continue. But that's not easy when the player himself is yelling he's OK and the doctors know that every minute they take is another minute the team must survive without that player.
And once a player is substituted, he can't return.
To give doctors more time, the world union for footballers is arguing that soccer's rules - first codified 151 years ago in a London pub - should be revised so teams can temporarily replace players while they're examined for possible concussion.
''It might take a medical practitioner at least 10-15 minutes to properly diagnose a possibly concussed player, and symptoms/signs can take longer than that to show,'' FIFPro said in emailed responses to questions from The Associated Press.
''Teams and players should not be disadvantaged for upholding player health and safety, or encouraged to act in a way that compromises it.''
FIFA's medical chief told the AP he doesn't oppose the idea. Michel D'Hooghe also was critical of Uruguay's management of a head injury to Alvaro Pereira in a match last week against England.
Pereira inadvertently got a knee to the temple. He later said the blow knocked him out and ''was like the lights went out.'' Team doctor Alberto Pan initially made hand signals for a substitution but then seemingly changed his mind after the clearly dizzy player furiously protested. The images provoked criticism from FIFPro, head injury specialists and others.
''I was also not happy with that situation. I must confess that,'' said D'Hooghe, a member of the FIFA executive and chairman of its medical committee.
D'Hooghe said one possible risk with temporary substitutions could be that players' muscles would cool while they're examined and this would make them more prone to injuries if they then are put back in play.
However, D'Hooghe said FIFPro's proposal ''has also advantages. ''
''It's a discussion point for the future,'' he said.
D'Hooghe also said FIFA should legislate procedures for managing suspected concussions. Currently, there are FIFA-approved guidelines team doctors can follow, but they're not obliged to do so.
''I think we can make that step forward, from guideline to rule,'' D'Hooghe said. . ''And we will do that.''
The team physician for Italy, Enrico Castellacci, agreed that football needs clear rules for head injuries. Castellacci used his authority in a pre-World Cup warm-up match to prevent Alberto Aquilani from playing on after an injury.
''There should be standardized protocols - at the national, European and international levels and that still isn't the case,'' Castellacci said.
FIFPro said to the AP: ''Binding regulations are required which ensure that player health and safety considerations override sporting ones.''
Players acknowledge they can be their own worst enemies. Belgium captain Vincent Kompany played out a World Cup qualifying match against Serbia last year with a broken nose, a fractured eye socket and light concussion.
''No one in my family was very happy with the fact that I kept on playing,'' Kompany recalled. ''I would always listen to what the medical staff has to say but, then again, I would do the opposite of what the medical staff would say.''
''You have to take emotions and adrenaline into account,'' he said. ''Unless someone puts on the emergency brake, you are not going to do it yourself.''
Uruguay officials turned down an AP request to interview Pan. Coach Oscar Tabarez explained Pan's hand signals for a substitution as ''a misunderstanding.''
Pereira was ''asked where he was, what he was doing, what was the score, and his answers were correct,'' the coach said. ''It's funny, if not dramatic, to think that we could have been careless.''
But he also acknowledged: ''We work against the clock.''
Headway, a brain injury association in Britain, doesn't want temporary substitutions. In an email to the AP, it said athletes shouldn't return to play at all on the day of a concussive injury. Instead, it suggests teams should simply be allowed to replace a player with a concussive injury, even if they've already exhausted their normal allotment of three substitutions.
Another potential issue with temporary substitutions would be ensuring teams don't fake head injuries to give players breathers.
Still, ''any rule change that gives medical staff more time to assess an injury and ensure player safety is a good idea,'' said Theron Enns, director of sports medicine and head athletic trainer for the Houston Dynamo in Major League Soccer, also responding by email to questions from the AP.
''The current difficulty for all medical staffs in soccer is how to accomplish that within the current context of a running clock and limited substitutions. ''
AP writers Andrew Dampf, Raf Casert, Bradley Brooks and Pablo Giussani contributed. John Leicester is an international sports columnist for The Associated Press. Write to him at jleicester(at)ap.org or follow him at https://twitter.com/johnleicester