Microphones picked up Arnold telling Josh Brilliante and Brandon O'Neill to get yellow cards in the second half of the Sky Blues' match against City on Saturday night.

Prior to getting booked, Brilliante and O'Neill were both one yellow card shy of suspension.

And by following instructions and copping another yellow, both players will now serve their one-game suspension this weekend, as Sydney face Wellington Phoenix, which ensures they're not ruled out of the finals.

Former Socceroos goalkeeper Mark Bosnich has defended Arnold for putting his team's finals campaign first.

"You have got to do what you have got to do," Bosnich told Fox Sports.

"If it's in the regulations, you have got a problem. If not, you haven't."

While the tactic has been banned in some European leagues, the actions don't break any domestic laws, Football Federation Australia said.

"Whilst the FFA is disappointed to note that Graham Arnold has instructed his players to deliberately seek a yellow card, it does not contravene the rules and will not be the subject of further investigation," an FFA spokesperson said.