(REUTERS) - English Premier League clubs on Thursday (Dec 17) agreed in principle to introduce additional permanent concussion substitutions, after the sport's rule-making body IFAB approved trials.

Representatives from all 20 clubs attended a shareholders' meeting, where they discussed the issue following IFAB's decision to give the go-ahead for trials on Wednesday.

The new rule will allow a maximum of two permanent concussion replacements in cases of head injury, regardless of the number of substitutions a team has made already.

The new protocols will also allow the opposing team to make an equivalent number of changes and the league has said it hopes to begin trials by January.

"The trial is a result of the IFAB's consultation with stakeholders and recommendations from their concussion expert group to allow additional substitutions for players with actual or suspected concussion," the league said in a statement.

"The league will now apply for permission from the IFAB, via the FA (Football Association), to take part in the trial which could be implemented as early as January 2021."

The shareholders also approved an amendment to the league's rules to increase the number of substitutes a club may include on their team sheet from seven to nine from round 14 until the end of the season.

However, the clubs voted against allowing teams to make five substitutions per match this season, a Premier League source told Reuters.

It comes after repeated calls from a number of top-flight managers - including Liverpool's Jurgen Klopp and Pep Guardiola of Manchester City - to protect player welfare amid a fixture schedule affected by the Covid-19 pandemic.

Yet the proposal once again failed to meet the threshold of 14 votes in favour at a meeting of the 20 clubs. Instead, the shareholders agreed to increase the number of players allowed on the bench from seven to nine. This measure will come into effect from matchday 14, which begins on Saturday.