Lealiifano looking likely to be the Wallabies' No.10 against England

Christian Lealiifano is firming as the Wallabies playmaker for their Rugby World Cup quarter-final after coach Michael Cheika shed some light on his erratic selection methods at five-eighth.

Cheika has been criticised for failing to select the same player in the No.10 in successive matches since Lealiifano started both Bledisloe Cup Tests in August.

The position has taken on an experimental feel in Japan, with Bernard Foley handed a start against Wales and Matt To'omua against Georgia.

Lealiifano started the first and third games, against Fiji and Uruguay, and while not entirely convincing, he appears set to run the show against England on Saturday.

Cheika indicated the 32-year-old's opportunities had been reduced because of his age and ongoing recovery from a leukaemia diagnosis in 2016, which still required careful management.

The Brumbies veteran took a year off rugby during the most intense part of his treatment and his Wallabies return this season marked the end of a three-year hiatus.

"We were always going into (the World Cup) thinking that we will share roles in that position," Cheika said.

"Obviously Christian hasn't played a lot of Test footy. He's been building and building and building from quite a serious illness and it takes time for him to get up to the levels that he needs to.

"I'm not going to throw him out there in every game, in every minute of every game, and say go 'slug it out'. The same at training, because you want him to keep his energy."

While Foley's form seems a shadow of his 2015 tournament prime, To'omua looked sharp at times in his five-eighth opportunity.

However, To'omua starred off the bench in the two biggest pool games against Fiji and Wales and appears likely to return to that role.

At halfback, Nic White has started three games and Will Genia one.

White is favoured to run out against the English, whose play he knows well after two seasons with Exeter.

The 29-year-old wouldn't identify which of the five-eighths he felt he had the best chemistry with in Japan.

"We chop and change since I've been back in June, in training, in games, and we feel as nines and tens there's plenty of different partnerships," White said.

"No matter who gets thrown in there, we feel comfortable to do the job for the team."