Toomua, O'Connor, Lolesio or Harrison: Who is leading the charge to start at No. 10 for the Wallabies?

Coach Dave Rennie is keeping his Wallabies on edge ahead of the opening Bledisloe Cup clash against New Zealand in Wellington, with the players in the dark on his starting line-up.

The No.10 jersey is the most hotly contested with four options - veterans Matt Toomua and James O'Connor, and rookies Noah Lolesio and Will Harrison - in the squad.

Toomua said he has been training at five-eighth and inside centre through their build-up in Christchurch, and tipped Rennie to go with a mix of youth and experience for Sunday's match.

That could mean Toomua at 12 and Lolesio to make his test debut at 10.

"I don't think anyone will be disrespecting the Bledisloe and naming a team full of debutants," Toomua said on Tuesday.

"But in saying that that we've got to develop players and develop a squad for the future so I'm sure it will be a balance and most guys probably guess it will be a mix of both."

The 30-year-old Toomua feels there is more competition at five-eighth than at any time during his 52-test career, adding it is "stressful" not knowing the new coach's plans.

"We're all waiting to see Dave's first squad; it's a bit of a blank slate with four options and all have played well," the 30-year-old said

"In the last few years we've had options at 10 as well but you just got an idea because we were later into the season, or you'd seen the way Cheika [coach Michael Cheika] liked to pick his flyhalves.

"At the moment it's pretty open, which is nice and stressful for guys like myself."

Toomua made a daunting test debut against the All Blacks in Sydney back in 2013 and said after a tense build-up he felt a "big relief" once it was over.

But he believes the new brigade of Wallabies will handle the occasion, particularly with their preparation occurring inside a quarantine bubble in Australia and New Zealand.

"They've got a ton of confidence and a lot of them have come from a winning team , particularly the Brumbies guys," he said.

"Someone like Noah [Lolesio] is a good example, he's just won a competition and he's got some good experience in big games under his belt."

The Wallabies will continue preparing in Christchurch and fly to Wellington on Saturday afternoon after their final training run.