Tottenham boss Ange Postecoglu does not think proposed plans to trial blue cards for sin-binned players will "make any difference" to the game.
Postecoglu says he "does not understand the urgency" to bring in new rules.
It comes as football's lawmakers Ifab delayed plans to release information about four proposed trials following talks with world governing body Fifa.
"A football match has a life of its own. There are mistakes, flaws and imperfections," said Postecoglu.
The Australian added: "I struggle to understand why there is this urgency all of a sudden to bring in new things. I don't know if there much wrong with the game as I see it and why a different colour card will make any difference.
"Most of the other sports are trying to speed up their game and I don't know why we are trying to go the other way."
When asked about the proposed trial, Liverpool boss Jurgen Klopp added: "It doesn't sound like a fantastic idea in the first moment. But actually, I can't remember when the last fantastic idea came from these guys [Ifab] - if they ever had one."
Fifa responded to multiple stories on Thursday, some of which raised the potential for the trials to involve elite football, with a public statement urging caution.
It is understood the four trials will remain following further consideration initiated by Fifa, but it has now been decided there will be no confirmation of the precise details until a media conference immediately after Ifab's annual meeting at Loch Lomond on 2 March to allow for "further exchange".
Fifa has four of the eight seats at Ifab, with the other four belonging to the home nations.
President Gianni Infantino has previously attended Ifab annual meetings. and If he does not attend, another senior official from the organisation will be present.
Sin-bins have been used at grassroots level for dissent but their use could be extended to cynical fouls as part of a trial.
A player would spend 10 minutes in the technical area after being given a blue card by a referee.
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