This post first appeared in Business Insider.

During the first half of Argentina's semifinals match, Javier Mascherano was wobbled and appeared to suffer a head injury when his head collided with a Dutch player while both attempted a header. Mascherano momentarily left the pitch but quickly returned.

A similar scene occurred during Uruguay's win over England at the World Cup as Uruguayan midfielder Alvaro Pereira was injured when his head collided with the knee of an English player. Even though he appeared to be momentarily unconscious, Pereira remained in the game, in large part because FIFA's antiquated substitution rules do not allow teams enough time to properly evaluate players for concussions. This particular case is a perfect example. It was clear to anybody with access to a replay just moments after the collision that the contact with Pereira's head was not only severe but that he was clearly out of it as he laid on the pitch:

Pereira was able to get up and walk off the field, but he was clearly woozy and a person who appeared to be the team doctor immediately signaled to the sideline that a substitute was needed:

But once Pereira saw the signal for a substitute he immediately argued that he was staying in the game, saying no to both the doctor and to the coaches:

After the match, the team doctor signed a statement saying he had completed a full neurological examination before allowing Pereira to return.

And here is where soccer has its biggest problem when it comes to head injuries.

The team's manager must make a decision right now, and he has three choices.

1. He can insert a substitute and lose one of his best players for the rest of the match. In soccer, once a player is replaced by a substitute he cannot re-enter the game.
2. He can have the player evaluated for a concussion. But this forces a team to play with only 10 players until the evaluation is complete. According to the NFL, a proper concussion evaluation takes a minimum of eight minutes and includes a test where a player must recall a specific word five minutes later.
3. He can just trust his player and put him back in the game at the next dead ball.

The Uruguayan manager opted for the third option, reinserting Pereira without a proper concussion evaluation. Most managers would make the same decision.

Former American national team member and current ESPN analyst Taylor Twellman was one who expressed his concern with how FIFA handles head injuries, saying "Any questions about Perriera being unconscious?! This has to stop FIFA."

While this particular injury was a freak accident, head injuries are not rare in soccer. Concussions are actually a huge problem because of headers in general and especially when two opposing players attempt to head the ball at the same time:

The simple solution is that FIFA is going to have to allow special temporary substitutions when a head injury is suspected, something already being tested in Rugby. Allow teams to enter a substitute while the injured player is tested along with a time limit on the return of the player (e.g. if the player is not cleared to return in 12 minutes, he cannot return).

To minimize abuse of the rule, these substitutions could count toward the allotted three substitutes. Another possibility is to give each team one such concussion substitution per match. Teams will still abuse the rule, but this is a risk FIFA must take for the safety of the players.

Like the NFL, a concussion crisis is coming to FIFA and the sport of soccer. Changes will have to be made that will affect the tradition of the sport. But those changes must be made.

Read all of Slate's World Cup 2014 coverage.

See Also: A World Cup Fan Gets a Modeling Deal