New Zealand Rugby has admitted Ireland prop Jeremy Loughman should not have been allowed back on the field during Wednesday's game against the Maori All Blacks after sustaining a heavy blow to the head.
Loughman went off for a head injury assessment (HIA) less than two minutes into the game, but returned having been passed fit to continue by an independent match doctor.
He was taken off permanently at half-time following advice from the Irish medical team.
"We have identified a gap in communications, which meant critical video evidence was not fully accounted for as part of the head injury assessment process undertaken by the independent match day medical team," said New Zealand Rugby medical manager Karen Rasmussen.
"We will be reinforcing the full HIA process and protocols for the remainder of the series to ensure video evidence is communicated more accurately between independent match day medical staff to enable them to make the right call with regards to player safety."
Munster loose-head Loughman appeared unsteady on his feet after the early collision and was temporarily replaced by Cian Healy.
He returned to the field to finish the first half, but the change was made permanent at the interval before Healy himself was forced off with an injury.
While Healy has been passed fit for a place on the bench in Ireland's first Test against New Zealand on Saturday, Loughman is unavailable as he continues to follow return-to-play protocols.
Last month World Rugby introduced new legislation that will see elite players face an increased minimum period of 12 days out of action following concussions.
Attempts to address the issues of head injuries and concussion within the game continue, with England's governing body the Rugby Football Union offering all players in the men's Premiership, women's Premier 15s and in England representative teams instrumented mouthguards that can help detect concussion.