RIO DE JANEIRO (AP) -- The world players' union accused World Cup organizer FIFA on Friday of failing to protect Uruguay midfielder Alvaro Pereira after he played on following a hard blow to the head he said felt ''like the lights went out.''
Pereira lay motionless after colliding with Raheem Sterling in the 61st minute of Uruguay's 2-1 victory against England on Thursday. He was allowed to return in the 63rd minute.
The union said that FIFA's protocol for assessing concussions ''failed to protect'' Pereira. It called for ''a thorough investigation'' as well as ''urgent talks and immediate assurances that FIFA can guarantee the safety of the players.''
Although Pereira himself acknowledged he was briefly knocked unconscious and then felt dizzy, FIFA spokeswoman Delia Fischer said: ''The neurological examination by the team's physician clearly showed that it's normal and that allowed him to return.''
FIFA and Uruguay's doctors will closely monitor Pereira, she said Friday.
FIFPro suggested possible rule changes so players suspected of being concussed can be temporarily substituted while they're diagnosed.
''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.''
When sliding for a ball, Pereira's temple inadvertently struck 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.''
Teammates surrounded the motionless player and signaled for a stretcher. Team medical staff came onto the field. Pereira wobbled to the sideline. Uruguay physician Dr. Alberto Pan signaled for a substitution.
Pereira seemed to have trouble maintaining his balance. He angrily wagged a finger to signal he didn't want to be substituted.
''I said 'sorry' a thousand times to the doctor because I was dizzy. It was that moment your adrenaline flowing in your body, maybe without thinking ... what I really wanted to do was to help get the result,'' the 28-year-old Sao Paulo FC player recalled. ''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 on whether he sustained a concussion, a subject that is slowly moving up the agenda in the sport.
FIFPro said it would monitor Pereira's health.
''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 said it also 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.
It added in-match concussion assessments ''must not be conducted solely by a national team physician.''
But FIFA's spokeswoman said: ''The ultimate responsibility lies with the team medical officer.''
In the English Premier League, Tottenham came under scrutiny in November for an incident involving goalkeeper Hugo Lloris. Currently with France's World Cup squad, Lloris was allowed to play on after he was briefly knocked unconscious colliding with Everton's Romelu Lukaku, despite medical advice he leave the match.
AP Sports Writer Graham Dunbar contributed from Rio.