Toomua said he had faith in the system and a month without rugby was "the best thing for my health" after he failed parts of the concussion test and officials stepped in to stop him returning to the field against Argentina two weeks ago.

Sideline concussion tests in rugby union and rugby league have been under the microscope with concerns over long-term player welfare and clubs putting players on the field when they haven't fully recovered.

Toomua suffered a heavy knock against Argentina and referee Nigel Owens forced him to leave the field for a cognitive test, which he passed, raising questions about the validity of its role in protecting players.

The ACT Brumbies star had also suffered concussion a week earlier in the Test against South Africa.

"I didn't lose consciousness, but I had a few other issues after the pitch-side concussion tests [with balance]," Toomua said.

"The second week was more severe. I had a few headaches and stuff like that. But I've got faith in the system. They ruled me out on the field, which was the right call, so now I've got a month off and that's the best thing for my health.

"I passed the test, but it was a bit weird to be honest with you ... my memory is sketchy of the test and the rest of the game.

"I had headaches and some memory loss ... but it's comforting from my point of view that the focus on head knocks and player welfare led to officials making the decision not to let me back on. It's a huge credit to the referee for recognising that and then the officials on the sideline as well."

Toomua has backed ACT Brumbies teammate Christian Lealiifano to replace him in the Wallabies' No.12 jersey against the All Blacks on Saturday night in his first starting XV appearance in more than a year.

Super Rugby and the IRB introduced more advanced sideline concussion tests this year, with the "head injury assessment" strengthening the memory test and altering the balance test to improve information available to doctors when deciding if players are safe to return to the field.

Toomua will return to the Wallabies camp for the spring tour if he shows no lingering symptoms.

"It was a heavy hit, I stayed down for a little bit because I was a bit rattled and there was a bit of whiplash there. You've got to have a long-term view on these things and my health."

Toomua admitted two knocks rattled him.

"It's a bit weird [when you get the knock]. You're not fully there or aware. I was lucky there were some good people in place to rule me out from getting back on the field.

"I don't doubt that people in the past got plenty of concussions, but in light of the new emphasis that we know about hits to the brain and how serious it is ... It's not all as grim as it's painted it out to be. But I think it's good there is a focus on player welfare."