LONDON: Wallabies coach Michael Cheika has implored his players to control their frustration at cynical breakdown tactics and to not lash out after David Pocock avoided World Cup disaster.

Pocock escaped with an official warning from the World Cup citing commissioner after he appeared to knee a Welsh opponent in the chest when trying to break free of behind-the-play tactics.

Pocock raised his knee as he tried to free himself and the incident was deemed worthy of meeting the off-field yellow card threshold.

The star flanker will avoid a potentially World Cup-ending suspension, but Cheika urged the Wallabies to keep their cool if they get dragged into negative tactics.

The Wallabies were under the pump against Wales and were penalised 12 times in the match, including having Will Genia and Dean Mumm sent to the sin bin.

Somehow the 13-man Wallabies managed to hold on and escape with victory, but Cheika conceded they were lucky and could not afford more costly mistakes.

"It's really hard for the refs to pick. We all love to be critical, but they're watching everything … it happens at a lot of rucks. We wouldn't be blowing up about it. It's just [a matter of] getting yourself out of there and get moving," Cheika said.

"That's the way the game is, it's changed a lot. And the strength of the game is discipline.

"You can't be playing the game with 13 against 15. We were lucky we got away with it. I don't think we were poorly disciplined, we just went through a little trot there where we made a few errors back to back and the way the game was going, we paid the penalty."

Citing commissioner Steve Hinds deemed Pocock in breach of Law 10.4(a) for striking another player with his knee. If he was cited and sent to face a judiciary, he could have faced a penalty of between four to 12 weeks.

But it was decided the incident involving Welsh hooker Scott Baldwin deserved an off-field yellow card, which will only come into play if Pocock gets two more yellow cards during the tournament.

Pocock is racing the fitness clock to be back on the field in time for Australia's quarter-final contest against Scotland on Sunday (Monday morning AEDT).

He will have scans on his calf on Tuesday and medical staff will determine how bad the damage is before deciding if he is available for selection.

Israel Folau (ankle) and Matt Giteau (ribs) are expected to recover in time, with Giteau and captain Stephen Moore set to play their 100th Tests.

Ireland flanker Sean O'Brien was involved in a similar incident being held behind the play, but O'Brien reacted and punched France lock Pascal Pape in the stomach.

"He [Pocock] got held a bit [against] Fiji as well. But if I was coaching against him I'd probably try to hold him as well," Cheika said.

Cheika conceded discipline would be crucial in the knockout stage of the World Cup, starting with Scotland.

He said Genia was apologetic for the yellow card he gave away for failing to retreat 10 metres, but backed the halfback's decision to make a potential try-saving tackle.

"I'd prefer to play with the full allocation of numbers. What I'd prefer to do is not give away the first penalty [which led to Genia's sin-binning], that was dumb by Adam [Ashley-Cooper] and he knows it," Cheika said.

"It's probably the way the game was going, dragging into that. That's not our go, we're not playing for that type of stuff.

"At the end of the day there's no excuses. And the way the guys are kicking now … the guys from France was kicking from 50-something metres … you've got to be so careful [with giving away penalties]."

WORLD CUP QUARTER-FINALS

Quarter-final one: South Africa v Wales at Twickenham, 2am Sunday AEDT.

Quarter-final two: New Zealand v France at Cardiff, 6am Sunday AEDT.

Quarter-final three: Ireland v Argentina at Cardiff, 11pm Sunday AEDT.

Quarter-final four: Australia v Scotland at Twickenham, 2am Monday AEDT.