All Blacks loose forward Luke Jacobson has been ruled out of the Rugby World Cup due to a delayed onset of concussion and will be replaced by Shannon Frizell, the team said on Friday.
The 22-year-old Jacobson had played just 20 minutes off the bench against Argentina before he was named in the squad for the tournament.
He came off the bench against Tonga on Sept. 7 and did not suffer any issues until the All Blacks arrived in Japan and he developed symptoms after their first training session.
"After discussing this latest episode with Luke, as well as our medical team, the decision has been made to, sadly, withdraw him from the tournament," All Blacks coach Steve Hansen said in a statement.
"We all felt that the best thing for him to do is to take a break from rugby until he is symptom-free.
"While it was a tough conversation to have, ultimately it was a very simple decision. Luke's health is the most important thing above anything else."
The highly regarded Jacobson had been one of New Zealand's form players in Super Rugby but after he made his debut against the Pumas he did not appear again due to concussion symptoms.
The former captain of the New Zealand under-20 side, however, told media last month that his symptoms were behind him.
He said on Friday he was "gutted" to be missing the World Cup.
"Whilst I'm feeling 98 percent OK, I know I'm still not quite right," Jacobson said. "By taking a break now, I'll give myself the opportunity to continue my career in the future."
Jacobson battled concussion in 2018 and only returned to rugby in March after eight months out of the game.
He told reporters in April that he had headaches for "four or five months" last year.
Frizell was in the original 39-man squad selected by Hansen this year as he narrowed his picks for the tournament and while he played against the Springboks in July, he was not included for two matches against Australia.
The 25-year-old had been playing in New Zealand's provincial competition, appearing as a lock, No. 8 and blindside flanker.
Hansen added that Dalton Papalii and Vaea Fifita, who also dropped out of World Cup contention earlier in the season, were not considered because of injury.