RIO DE JANEIRO -- The world players' union FIFPro has accused FIFA of failing to protect Uruguay defender Alvaro Pereira after he played on against England following a blow to the head.
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Pereira lay motionless after colliding with Raheem Sterling's knee in the 61st minute of his side's 2-1 Group D win on Thursday.
The 28-year-old appeared dazed and not fully aware of his surroundings, but was still allowed to return to the field in the 63rd minute.
FIFPro has urged FIFA ''to conduct a thorough investigation into its own competition concussion protocol, which failed to protect Uruguayan footballer Alvaro Pereira.''
It asked for ''urgent talks and immediate assurances that FIFA can guarantee the safety of the players.''
The union also suggested possible rule changes so players suspected of being concussed can be temporarily substituted while they are examined.
''Football is awash with incidents in which players suffer potentially concussive blows to the head and stay on the pitch. In Pereira's case, he demanded to play on, overruling advice from Uruguay's team physician for him to be immediately substituted,'' FIFPro said in a statement.
''FIFPro understands that in certain moments, faced by the pressures of such an important international stage, many players would react in this way. There are times, however, when the players also require greater protection against the prospect of making any rash decisions.''
As he slid for a ball just outside Uruguay's penalty area, Pereira's temple inadvertently collided with Sterling's left knee.
''After the hit, I only recall that I was unconscious for an instant,'' he said.
''It was like the lights went out a little bit," the Sao Paulo player was quoted as saying by Associated Press.
Teammates surrounding the motionless player signaled for a stretcher before Uruguay's medical staff came onto the field.
Pereira wobbled to the sideline, with Uruguay physician Dr. Alberto Pan signalling for a substitution.
However, despite seeming to be having trouble maintaining his balance, Pereira argued and angrily wagged a finger to indicate that he did not want to be taken off.
''I said 'sorry' a thousand times to the doctor because I was dizzy. It was that moment your adrenaline is flowing in your body, maybe without thinking ... what I really wanted to do was to help get the result,'' he said.
''What really matters is that everything is OK. Nothing happened, it was just a scare."
Pereira said a team doctor and a FIFA physician checked him after the match.
There was no immediate confirmation, though, on whether he suffered a concussion -- a subject that is slowly moving up the agenda in football.
FIFPro said it would monitor Pereira's health on Friday.
''He must be subjected to further evaluation and follow-up procedures that help determine if and when he can return to training,'' it said.
The union added that it is considering appointing its own independent doctors ''for all future FIFA competitions.''
''The World Cup must set the standard for player health and safety to educate the international football community. Medical evidence shows that a person faces the risk of very serious brain injury, or worse, if he or she suffers a severe head trauma from a concussive blow,'' FIFPro said.
''Furthermore, FIFPro states any sideline concussion assessment must not be conducted solely by a national team physician. In order to ensure real independence, FIFPro's involvement, as the international authority representing the interests of the players, would ensure they are insulated at all times.''
Tottenham came under scrutiny in November for an incident involving goalkeeper Hugo Lloris.
Currently with the France squad at the World Cup, Lloris was allowed to play on -- despite medical advice stating he should come off -- after he was briefly knocked unconscious following a collision with Everton's Romelu Lukaku.