Alvaro Pereira was allowed to continue playing in Uruguay's FIFA World Cup clash with England on Thursday, despite appearing to be unconscious for a period.
Uruguay's team doctor Alberto Pan originally signalled to the bench for the full-back to be withdrawn, yet Pereira's wish to remain on the field was granted.
"Football is awash with incidents in which players suffer potentially concussive blows to the head and stay on the pitch," said FIFPro 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."
FIFPro have also again expressed concern over what they feel is a failure to protect players from heat in Brazil.
A second statement read: "Ahead of this weekend's World Cup matches in Fortaleza and Manaus, FIFPro is concerned the players are not receiving adequate protection as their cries for help continue to fall on deaf ears.
"The heat and humidity in the north of Brazil is proving quite a challenge for the players who, by their own admission, are clearly suffering in the conditions.
"Even when faced by mounting evidence and strong views presented by the players, FIFPro sees a reluctance that FIFA is willing to adapt. What will it take for the players' views and their health to be taken seriously?"
