Michael Cheika has defended the intentions of coaches and team medicos after withdrawing Test hooker Tatafu Polota-Nau from the Waratahs' clash with the Blues on Saturday.

Polota-Nau suffered a head knock in training last week and missed his team's spiteful derby win against the Brumbies on Sunday, but was named on the bench to face the Blues this weekend after training symptom-free early in the week.

He was withdrawn on Wednesday, after experiencing symptoms during the team's training session at Newington College on Tuesday.

Cheika said there was no debate about whether to play him or not, regardless of strict global protocols governing a players' return to play after a concussion.

"Everyone else in their whole concussion debate, it's almost like they've put in lots of rules because they think the coaches don't care," he said.

"But it's the absolute opposite. The players are our biggest asset so why would we go out and risk them.

"'Taf' wasn't feeling 100 per cent after training the other day so there was no question ... we could have in fact let him hang on until Thursday and see how he went but we've got to back our other guys."

Concussion is a controversial topic in contact sports and, in rugby, has been the subject of rapid reform.

The sport's global governing body, World Rugby (formerly the International Rugby Board), has progressively tightened protocols over the past two years and handed extensive new powers of review and removal to match officials and medicos.

This is the first season the rules apply in Super Rugby and it did not take long for their first practical test. Kurtley Beale took a head knock in round two and played on, but was pulled off the field some minutes later for a concussion test by ARU medical consultant Warren McDonald.

McDonald had used the new protocols to ensure Beale was not suffering the effects of concussion. He had replayed the incident on a pitchside monitor and made the decision to call for the player's removal. Beale passed a concussion test during the match and was allowed to play on.

Beale was slightly bemused by the process in the aftermath of the match, and Cheika said on Friday he had no problem with the protocols but expected their implementation would take some months to perfect.

"They're learning how to use that [the new powers], it's only relatively new," he said.

"They're always going to err on the side of caution ... I think as they learn as they use it and get some consistency amongst the doctors on what they see, it'll be fine because then they can explain it to the coaches."

Polota-Nau will be given the bye round to complete his recovery and is expected to return to play in round nine, alongside centre Adam Ashley-Cooper (knee).