Pocock has been cleared to play in the semi-final against Argentina at Twickenham on Sunday (Monday morning AEDT), ensuring the Wallabies avoided the dreaded question of can they win the World Cup without him.

Less than a year after making his comeback from two knee reconstructions, Pocock has established himself as the most crucial player in the Wallabies' line-up.

Four World Cup-winners are united in the belief that Pocock's presence looms as the game-breaking factor for the Wallabies' dreams.

England World Cup champion Lewis Moody declared Pocock "without a doubt" the most important player left in the tournament as the four remaining teams fight for spots in the final.

But former Wallabies coaches Rod Macqueen and Bob Dwyer are adamant Pocock doesn't solely shoulder Australia's hopes.

The statistics tell the story of Pocock's impact in international rugby. Pocock's Test winning percentage is 65 per cent, but in the two years he was out injured the Wallabies slumped to a win-rate of just 46 per cent.

He has lost just once in the gold jersey since making his comeback from two knee reconstructions.

"When he's not there, Australian definitely miss him. Without a doubt he's having a big World Cup influence and given his importance you'd say the most influential," Moody said.

"Once he gets on the ball at the breakdown, he's almost impossible to move. Even more than [New Zealand captain] Richie McCaw.

"He's the key to unlocking Australia's gifted back line because he can turn the ball over. If Australia don't have that, then they don't seem to fire and that directly correlates to whether Pocock's there."

Pocock has already stamped himself as one of the most dominant players at the World Cup, leading the tournament turnover statistics despite playing just three of the Wallabies' five games.

It's a remarkable turnaround after a shattered Pocock ruptured his anterior cruciate ligament twice in less than a year and missed almost two full seasons of Super Rugby.

But you won't find the 27-year-old lapping up the attention of the World Cup hype.

He has been spending his spare time exploring London and visited a photography exhibition at the National History Museum to escape the semi-final build up.

It showed his relaxed nature ahead of one of the biggest games of his career and his race against time to be fit.

Pocock's absence hit hard in the Wallabies' narrow quarter-final escape against Scotland last weekend as Australia struggled at the breakdown and forced just two turnovers.

"In the modern game, turnover ball is really critical. You don't get many attacking opportunities unless you get turnovers," said Wallabies' 1991 World Cup-winning captain Nick Farr-Jones.

"David Pocock is the best in the world at producing that. In my view, he is the best in the world at the breakdown, pinching ball, and that's the best attacking platform you have.

"If you're picking a world XV back row right now, you couldn't leave David Pocock out.

"If by chance, we play New Zealand in a World Cup final, Richie McCaw will dread playing against a back row with David Pocock, Michael Hooper and Scott Fardy. It would be one of the hardest tasks in world rugby."

Many questioned whether the Wallabies needed Pocock after Hooper emerged as a star, claiming the No. 7 jersey and rising to the Test captaincy.

Hooper is a defensive machine and an attacking weapon, but doesn't possess the same breakdown presence of Pocock.

Memories of Pocock's 2011 quarter-final heroics act as the reminder of his importance to the Wallabies' World Cup hopes.

He has continually delivered when Australia has been under the pump, putting his head in "dark places" to win the ball.

The Wallabies struggled to find leadership before Cheika took over as coach. But Australia's 1999 World Cup-winning coach Rod Macqueen said the triple return of Pocock, Matt Giteau and Stephen Moore has added the maturity needed to rise to the top of the world.

"I think Pocock and [Matt] Giteau add the maturity to this team. Injuries always happen in World Cups and Australia has great depth, so if Pocock is not there they can cover that," Macqueen said.

"I don't think Pocock being there or not will change the way they play. Pocock has a massive influence and you need those sorts of players, but of all the positions, if Pocock is out, we have some good reserves there."

Workhorse Ben McCalman stepped up to replace Pocock last weekend and Sean McMahon is waiting for his opportunity.

"But you'd obviously like to have more world-class players starting in your team," said 1991 World Cup-winning mentor Bob Dwyer.

"Pocock would be very useful, that's for sure. But you want to be able to do it without him as well and I think we should be able to.

"I'd love to have Pocock for this weekend and for the final if Australia gets through. He's a different player. Hooper is good over the ball, Pocock is outstanding. But yes, Australia can win if he's not there."

Moody said: "Just the fact that Pocock is back is a testament to his mental resilience, coming back and fighting back at the same level you left at is amazing.

"Whenever we played against him, it was always a plan to try to move him off the ball.

"Fingers crossed for Australia that he's there this weekend."