The France international was caught in the head when he collided with Romelu Lukaku late on in Sunday's goalless draw.
He later underwent a "precautionary CT scan" that Spurs confirmed was clear but manager Andre Villas-Boas's decision to let him stay on the pitch because he seemed "composed and ready to continue" has provoked widespread condemnation.
FIFA's chief medical officer Professor Jiri Dvorak said: "The player should have been substituted. The fact the other player needed ice on his knee means it's obvious the blow was extensive.
"It's a 99 per cent probability that losing consciousness in such an event will result in concussion."
Dvorak later told Sky Sports News that the player's opinion should not have been taken into consideration.
"The opinon of international experts - including myself - is that if there is an obvious concussion, the player should be taken out of any sporting activity and should be medically assessed," Dvorak said.
"If there is a medical problem, the decision must be taken by medical personnel. Particularly with concussion, you don't know if the player is in a state to make the decision by himself. The manager is not aware of the medical background.
"A direct blow of the knee to the skull can lead to bleeding in the skull cavity and this is potentially dangerous. If there is doubt, keep the player out."
Tottenham's head of medical services, Wayne Diesel, told the club's website on Monay morning: "Once the relevant tests and assessments were carried out we were totally satisfied that he was fit to continue playing."
But further criticism came from the world players' union, FIFPro, medical advisor Vincent Gouttebarge saying: "This decision is unacceptable. FIFPro condemns that the health and safety of players are let to coaches/trainers or even to players themselves."
The deputy chief executive of the Professional Footballers' Association, John Bramhall, said football had to remove the decision-making process when a player had lost consciousness.
Bramhall said: "When treating a player on pitch, it can be very difficult to determine the severity of a head injury. It is important to take the pressure off the players, club medical staff, and the manager - removing the need for them to make a very difficult decision."
"If anyone suffers a severe trauma to the head and loses consciousness, then they should be required to leave the field of play automatically."
Leading brain injury charity Headway said the club displayed a "cavalier" attitude to the player's health.
Headway CEO Peter McCabe told Sky Sports News: "If someone has been knocked out on the pitch then they should be removed and properly assessed. Asking the player if he is ok is ludicrous, it seems to us.
"You risk so much - no-one can see inside somebody's skull. It is dangerous and irresponsible to leave someone in that situation."
McCabe said he is in no doubt who should have the final say on whether a player continues or not.
"It always has to be a medic. It can't be the player because the natural inclination of a footballer is that they want to continue. His manager described him as showing real character. To me that isn't a decision a player should make.
"He wasn't in a fit state to make that decision. It was quite apparent that some of his team-mates, having seen that sickening collision, were encouraging him to go off. And they had a perfectly adequate replacement waiting to come on. So it seems ridiculous that he should be placed in danger in that way.
"We think the FA needs to give clearer guidance to clubs. If somebody is knocked out we believe the FA should have a protocol that requires the player to leave the pitch and be properly assessed."
The FA has detailed regulations on head injuries and concussions, and the rules state that anyone suffering unconsciousness should not play again that day.
The FA regulations state: "Any player remaining immobile and unresponsive to verbal commands following a head injury will be regarded as being unconscious and treated in accordance with established principles for extrication and management of the unconscious player. There will be no return to play during that day."
The rules do however allow for "a transient alteration of conscious level" following a head injury, which says a player can return to play following assessment by medical staff.
"The player will only be allowed to resume play if asymptomatic and with normal co-ordination. The medical attendant should alert the coaching staff, and the player closely observed for any deterioration in playing ability," the regulations say.