Brain injury campaigners say they are "bitterly disappointed" after global football bosses rejected calls to hold a trial of temporary concussion substitutes in the Premier League next season.
The International Football Association Board (IFAB) met at Wembley to discuss the possibility of a trial after a request from world players' union FIFPRO and the World Leagues Forum to test the protocol in the Premier League, France's Ligue 1 and America's Major League Soccer.
However, Football Association chief executive Mark Bullingham, who supported the idea of a trial, said the group could not reach a consensus, saying: "There were very strong and very different views in the room."
"We agreed that it would remain under active review," he added.
Focus would now be on improving the effective implementation of the permanent concussion substitute protocol, he said.
However, brain injury campaigners believe temporary concussion substitutions would give players the best protection.
Luke Griggs, chief executive of the charity Headway, said it was "hard to fathom the flawed logic" behind the latest decision.
"The argument for the continuation of the current system appears to be that permanent concussion substitutes prevent injured players from returning to the pitch and therefore is a safer system.
"But this completely misrepresents the benefits of temporary concussion substitutes."
He added: "Temporary subs would allow medics more time to assess a player in the quiet confines of a dressing room.
"As the symptoms of concussion can be delayed in their presentation, a 10-minute assessment will never be perfect, but it is better than giving medics the impossible job of having to make snap judgements within two or three minutes under the intense pressure and glare of tens of thousands of fans in the stadium and millions more watching at home, as is currently the case."
He also said that if a player does display symptoms having returned to play after passing an off-pitch assessment, there is nothing to stop the temporary substitution being turned into a permanent one.
Bullingham said the concussion debate was the "longest conversation" in a meeting which overran by about 90 minutes.
But when asked whether a Premier League trial could still happen next season or had been pushed further away, he said: "It's been pushed further away."
The permanent concussion substitute trial will instead continue indefinitely.
The FA had been co-ordinating international efforts to get a temporary concussion trial approved and gathered the other three UK football associations for a meeting on Monday, where it is understood a majority were united in support of a protocol being trialled.
However, the fact that no consensus could be reached indicates FIFA - the other constituent of IFAB - remains convinced that the permanent concussion substitution trial is the best approach.
IFAB is comprised of the four British football associations (England, Scotland, Wales and Northern Ireland) with one vote each, and FIFA, covering the remaining 207 national associations, holding four votes.
FIFA conducted a survey of team doctors that had adopted the trial and found that 71% supported the permanent concussion substitute model.
The Professional Footballers' Association's head of brain health, Dr Adam White, described the failure to implement temporary concussion substitutions as "extremely disappointing".
He said: "We believe the introduction of temporary concussion substitutes is now increasingly seen as a common-sense measure to better protect players.
"Many will rightly ask "if not now, when?"