Tottenham manager Ange Postecoglou says the possible introduction of blue cards and sin-bins will “destroy” the game.
Football’s lawmakers Ifab delayed plans to release information about four proposed trials after talks with world governing body Fifa.
Under the plans, players would get blue cards for dissent and tactical fouls and spend 10 minutes off the pitch.
“Adding another [card] one. What is that going to do? The remedy is already there,” said Postecoglou.
“If it’s not being enforced to the level people are satisfied, do that. That’s the change. One team being down to 10 men for 10 minutes, you know what that is going to do to our game? It’s going to destroy it.
“You’ll have one team sitting there trying to waste time for 10 minutes waiting for someone to come back on. Every other game is trying to speed up and declutter, all we are trying to do is go the other way for some bizarre reason.”
If passed into the laws of the game, the introduction of a blue card would mark the biggest single change in managing player discipline since red and yellow cards came into force at the 1970 World Cup.
However, the Australian’s forthright views on the topic were also echoed by Liverpool manager Jurgen Klopp, with the proposals seemingly getting little traction among Premier League managers.
“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,” Klopp said.
Meanwhile, Newcastle boss Eddie Howe, added: “I’m not a big fan, to be honest. I think that’s what yellow cards are for. I think the current system works well, it’s just got to be applied right.
“Adding a blue card would just add more confusion, in my opinion. I’m against it. I think [sin-bins] would change it a lot, but again not, for me, in a good way because I think it will make it very bitty, more stop-start.”
Speaking earlier, Postecoglou also questioned the motivation to introduce new rules: “I struggle to understand why there is this urgency all of a sudden to bring in new things. I don’t know if there’s much wrong with the game as I see it and why a different colour card will make any difference.”
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. 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.
- Our coverage of your Premier League club is bigger and better than ever before – follow your team and sign up for notifications in the BBC Sport app to make sure you never miss a moment
