Major League Soccer will keep on pushing the sport's international rules-makers to allow a trial of temporary substitutes for players suspected of concussions.
The International Football Association Board, which decides rules, said Saturday that it will continue with trials of permanent substitutions for players suspected of head injuries. MLS and England's Premier League proposed having injured players be assessed for a longer period and have the potential to rejoin the match.
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"We strongly believe in the benefits of conducting the trial and welcome the opportunity to share the data and learnings from such a trial with the global soccer community," MLS said in a statement Tuesday.
"The proposed temporary concussion substitution protocol was developed with MLS's medical advisers and would allow club medical professionals to conduct a structured off-field evaluation of players suspected of sustaining a concussion."
The MLS Players Association has criticized the IFAB, which includes four representatives from FIFA and one each from the governing bodies of England, Scotland, Wales and Northern Ireland.
MLS said it will work with the Premier League, the French league, the MLS union, the international union FIFPRO and the World Leagues Forum to push the IFAB to trial temporary substitutes.
"In the meantime, we will continue to evaluate our options as we work with our players and clubs on implementing our current MLS head injury/concussion evaluation and management protocol," the league said.
MLS commissioner Don Garber said last month that the league was powerless to act without IFAB approval. He maintained the league was willing to innovate and cited adoption of video review in 2017 as an example.
"I get it. The global game has got to have the same rules and it's not as easy for us just to introduce on our own," he said. "We want them to do it. We'll be the first league to say we'll do it, like we tested VAR, the first league to do that, and now that's obviously embraced throughout the sporting world. But I'm optimistic and hope."
Defending their decision, FIFA director of medical Dr. Andrew Massey said this week that permanent substitutions for suspected concussions were safer than temporary ones.
"Brains suffer whenever they get injured, but they suffer exponentially more whenever they get another injury on top of that initial one," he told FIFA's website. "We want to decrease the likelihood of these false negatives.
"Having temporary subs, we've seen in the literature, will have the chance of a false negative of anything in the region of 16-25%. So, we'd be returning one in four people who do have a concussion, but it just hasn't manifested itself yet.
"So, we want to get a safer threshold. We want to change the narrative with respect to what everyone agrees with, not: 'Is this person concussed?' Rather: 'Can we rule a concussion out?'
"That's why the permanent subs are so much safer: zero chance of a false negative and zero chance of taking a risk with anybody that you suspect has a concussion, either from whatever symptoms they're displaying at the time, or the mechanism of their injury."
Information from the Associated Press was used in this report.