Players' union FIFPro on Friday urged an urgent review of the protection levels afforded to players with concussion after Uruguay's Alvaro Pereira suffered a sickening head injury in the World Cup clash with England.

Pereira collapsed to the ground and lay motionless after appearing to be knocked out after Raheem Sterling's knee collided with his head in the 61st minute of the Group D game in Sao Paulo which Uruguay won 2-1.The 28-year-old insisted on carrying on playing despite the Uruguay team doctor demanding he be substituted.

"Football is awash with incidents in which players suffer potentially concussive blows to the head and stay on the pitch," the players' union said in a statement on Friday."In Pereira's case, he demanded to play on, overruling advice from Uruguay's team physician for him to be immediately substituted.

"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. He must be subjected to further evaluation and follow-up procedures that help determine if and when he can return to training.

"The World Cup must set the standard for player health and safety to educate the international football community," the statement continued."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."