RIO DE JANEIRO (AP) - The players' union is accusing FIFA of failing to protect Uruguay midfielder Alvaro Pereira after he took a hard blow to the head against England at the World Cup.

FIFPro wants a FIFA investigation and possible rule changes so players suspected of being concussed can be temporarily substituted while they're diagnosed. Pereira lay motionless after colliding with Raheem Sterling's knee in the 61st minute of Uruguay's 2-1 victory on Thursday.

MORE: Pereira gets knocked out, ignores trainers, returns immediately

Even though he appeared like a punch-drunk boxer, Pereira ultimately was allowed to return to the pitch in the 63rd minute.

In a statement on Friday, FIFPro urged FIFA ''to conduct a thorough investigation into its own competition concussion protocol, which failed to protect Uruguayan footballer Alvaro Pereira.'' It wants ''urgent talks and immediate assurances that FIFA can guarantee the safety of the players.''

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