The Premier League is still waiting to receive updated protocols which will enable it to fix a start date for a concussion substitutes trial, the PA news agency understands.
Top-flight clubs agreed on December 17 to implement a trial which would allow a team to make up to two additional permanent substitutions in the event of a suspected concussion, with the opposition being afforded the same number of changes.
The league's medical working group met the following day to further discuss the protocols, but it is understood the league has not received the detailed, extensive list of requirements from the International Football Association Board. The Premier League needs this so that it can confer with clubs and check they are all able to meet the guidelines set out before confirming a start date for the trial.
A statement from the Premier League on December 17 said the trial could begin "as early as January 2021", and it remains possible that it will start next month depending on when the protocols are received.
The PA news agency has contacted the IFAB for comment.
IFAB approved the two-substitute protocol on December 16, and on the same day the Football Association said it would introduce it for the men's and women's FA Cups, the Women's Super League and Women's Championship at the earliest possible opportunity.
The national governing body is yet to confirm precise dates for the trial to begin, with the men's FA Cup third round getting under way on January 8 and the women's second round on January 3. Again, it is understood to be awaiting the required information from the IFAB.
IFAB has also approved a protocol where a team can make one additional concussion substitute but there is no reciprocal change given to the other team.
IFAB's updated concussion protocols were criticised by brain injury charity Headway, which says a longer assessment period for the player suspected to have suffered a concussion combined with temporary substitutes is a better approach.
Dr Willie Stewart, one of the leading experts on the neurological impact of concussion and heading, described the protocols as being akin to "putting lipstick on a pig".
FA chief executive Mark Bullingham said on December 16: "I'm really surprised this is seen as a cop-out. I see this as going further.
"We're taking any player that is suspected of concussion off the pitch. I don't follow the logic there.
"I understand there are two models that have got different values, but, from our point of view, we see this as a stronger model, the safer model, and that's what we're being advised by the medical experts."
