World Rugby has hit back at safety campaigners who criticised the professional game's head injury assessment (HIA) process.

Sexton was taken off during last Saturday's Test with a head injury, but passed subsequent stages of the HIA process.

"It is the duty of any individual or organisation commenting on the head injury assessment process to do so using the facts," said a World Rugby statement.

"Attempting to diagnose a serious medical condition like concussion from afar, without all the relevant information including a player's medical history, is irresponsible and no substitute for the world leading medical care received by elite rugby players.

"Doctors are supported by the head injury assessment and recently updated return-to-play protocols put in place by World Rugby. These protocols are developed using scientific evidence and independent expert opinion which are kept under constant review, as we never stand still on player welfare."

Sexton's head injury came a day after World Rugby's new laws on concussion came into effect, under which the majority of players diagnosed with concussion face an increased minimum period of 12 days out of action.

World Rugby's head injury assessment process has three stages - the first (HIA1) is an assessment at the time of the injury, the second (HIA2) is carried out two hours later, and the third (HIA3) completed 36 hours after the incident.

Ireland captain Sexton passed his second assessment - HIA2 - after being removed from the action last Saturday, before being declared fit on Tuesday following his third and final assessment.

"Elite players who fail an in-game HIA1 have, by definition, displayed cognitive dysfunction requiring their removal," said a Progressive Rugby spokesperson on Thursday, after Ireland's team for the second All Blacks game was confirmed.

"In our view, this is sufficient evidence, regardless of subsequent testing, to exercise extreme caution for the good of both their short and long-term health.

"This caution must be further amplified in players with a history of brain injury, as evidence is they are at higher risk of sustaining further concussions and other injuries."

Ireland began their tour of New Zealand with a game against the Maori All Blacks, during which prop Jeremy Loughman returned to the field after coming off for an HIA.

New Zealand Rugby admitted after the game that Loughman should not have been allowed to come back on despite being passed fit to continue by an independent match doctor, saying a "gap in communications" had been identified which meant critical video evidence was not accounted for.

The prop was subsequently ruled out of the Test opener.

"Concussion in elite rugby is formally diagnosed by qualified doctors at the HIA2 and HIA3 assessments as part of the Head Injury Assessment protocol, with the exception of any player displaying obvious symptoms who will be immediately removed from play," World Rugby continued.

"The in-game HIA1 off-field assessment combines video review and clinical observation to determine suspected concussion and informs the need to remove a player as a precaution.

"Any player who has not displayed obvious concussion symptoms and who compares to a pre-recorded baseline on HIA2 and HIA3 assessments, which take place two and 36 hours after an incident respectively, is deemed by medical professionals to be clear of concussion."