Jan Vertonghen's injury was the latest flash point to call attention to football's treatment of head injuries. Marc Atkins/Getty Images

The issue of head injuries in soccer -- and how to diagnose them -- has received more attention in recent weeks. The handling of an incident involving Tottenham Hotspur defender Jan Vertonghen, who returned to the field in the first leg of the Champions League semifinal against Ajax after suffering a head injury, was criticized in some quarters after the player nearly collapsed shortly after being cleared for play.

Now, a league is prepared to take the on-field diagnosis of head injuries to a new level. The United Soccer League, which contains leagues in the second, third and fourth tiers in the United States and Canada, has submitted a prospective rule change to the International Football Association Board (IFAB), the body that determines the laws of the game in the sport, that would allow for a "head injury substitution." This would allow teams to more carefully examine players with head injuries without having to burn a full substitution.

The USL's aim is to have the rule in place in the second-tier USL Championship and third-tier USL League One -- assuming IFAB approves the rule -- in time for the 2020 season.

"It's a safety issue, and we want to make sure that we're doing everything that we can do to protect the safety and well being of the players," USL president Jake Edwards said about the proposal. "That's it. It's that simple. As we've seen what's going on in the leagues around the world with some high-profile incidents lately, it's important that we come up with a plan that gives the medical personnel the appropriate time to properly assess the potential for head injuries."

At the professional level, teams are limited to three substitutions per match with no reentry. Once a player is substituted, they cannot return. This puts managers and medical personnel in a difficult position when it comes to serious injuries. Managers don't want to use a substitution unnecessarily, but they also don't want their team to be playing short, which is what happens when an injured player is taken off the field. Medical staff are put in the awkward position of trying to satisfy two masters, the team and the player. In the case of head injuries, too often players who are in no condition to continue playing are sent back onto the field.

The rule, as proposed, would work in the following manner: If a player on a team suffers a head injury during a match, the team can use a temporary substitute to take his or her place. This would allow for the injured player to be properly assessed without forcing his or her team to play shorthanded. The substitution can take place even if the team has used all of their allotted substitutions. If the injured player is deemed healthy enough to continue, they can reenter the match in place of the injury substitute. If not, the injury sub stays on the field and is made permanent, unless all of the allotted subs have been used. In that case, the injury substitute would have to come out of the game.

The current application to IFAB, submitted on April 17, doesn't yet contain a cutoff time for when a decision must be made in terms of the head injury sub being made permanent. But Edwards said there are plans to amend the application.

"I think there will be a cross-off period," Edwards said. "You can't have it be 15-20 minutes. I think there's [something] in the 10-minute range would be a good cutoff. We'd like to make a diagnosis between seven and 10 minutes. We're certainly going to look at that."

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For Taylor Twellman, this has been a cause he has championed since his own career was ended at age 30 by a series of concussions. In addition to his duties as an analyst on ESPN's soccer broadcasts, he has been a proponent for increasing awareness on the diagnosis and treatment of concussions through his advocacy group (ThinkTaylor.org).

Twellman didn't hold back in his assessment of how the Vertonghen incident was handled, calling it "pathetic" how the player was initially treated, taken to the sideline, and then allowed to reenter the match, only to have to come off after just 40 seconds and nearly collapsing on the sidelines.

"Vertonghen had two signs on [FIFA's concussion] protocol, that means come out of the game," he said. "I watched it 10 times, I've seen every clip. How did they follow the protocol if they were dealing with the blood coming out of the nose? So when they say they followed the protocol and gave it enough time, that's actually impossible because you were actually dealing with the bloody nose."

Yet Twellman, who was consulted by the USL before submission of its rule-change proposal, lauded the step taken by the league.

"The USL is being proactive with an issue that is still massively underappreciated and not understood," Twellman said. "The lack of understanding with the injury ... look at Tottenham in the Champions League. That in a nutshell tells you where we are with the game around the world. I don't think people are taking this seriously enough."

There is also support from FIFA, with the governing body's Medical Committee chair Michel D'Hooghe telling the Times of London that the organization is "prepared to discuss" introducing concussion substitutions.

Yet this is no knee-jerk reaction by the USL. Its proposal has been in the works for two years following a symposium on head injuries conducted by the U.S. Soccer Federation and MLS, with Twellman among the speakers. Following that symposium, Brett Luy, the head of the USL's competition committee, put together a task force comprised of doctors and athletic trainers to look at player safety, with head injuries a point of emphasis. Luy presented the plan for the head injury substitute last summer with the formal application made to IFAB last month.

This also isn't the first time the USL has been on the bleeding edge in terms of the game's rules. The USL was the first professional league to use Video Assistant Referee (VAR) in 2016, and it was based on its use through the 2017 campaign that MLS adopted it following year. Edwards is hoping for a similar outcome with respect to the head injury substitute.

"I think if we do this, we'll learn a lot and you'll see a lot of other leagues follow," he said.

There are still plenty of decisions to be made and work to be done. Edwards is keen to get on-field diagnoses done as quickly as possible, and is looking at technologies to help in that effort. There is also a need to have a standardized protocol, including setting up a proper environment for players to be examined at every venue in the league.

Then there is the tricky decision surrounding medical personnel. There have been calls for neutral doctors to make the decision as to whether a player should continue, but team doctors know the players best, and are better positioned to determine how seriously a player has been injured. Twellman is of the belief that both neutral and team doctors should collaborate on any decision.

"To just say you want neutral doctors making the decision, that doesn't actually cure the problem," Twellman said. "Now, a neutral doctor will enhance the process and here's how. What no one in MLS or any league or FIFA wants to tell you is that when I'm in a TV booth, that TV truck has multiple, multiple camera angles. It is humanly impossible to see all those angles, with two eyes, when you're sitting on the bench.

"So the final say should always be the one that knows that player. But a neutral doctor will only enhance that process and give some clarity to some situations that is humanly impossible for a team doctor to see on a sideline."

Edwards notes that most USL teams have partnerships with local medical providers rather than full-time medical staff, so a decision will need to be made at some point who will make the ultimately decision.

"We have to look at, as this grows, and as our league continues to grow, what is the best model," Edwards said.

For now, at least, a step forward in the diagnosis of head injuries has been taken. The USL is hoping that IFAB will allow them to take it even further.