New Zealand forward Luke Jacobson has been ruled out of the World Cup in Japan due to a delayed onset of concussion.
The 22-year-old won his second All Blacks cap in last weekend's 92-7 crushing of Tonga and travelled with the squad to Japan, but developed symptoms after their first training session.
Jacobson has been replaced by the Highlanders' Shannon Frizell.
"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," said New Zealand head coach Steve Hansen.
"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."
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 New Zealand U20 captain, who told media last month that his symptoms were behind him, said he was "gutted" to be missing the World Cup.
"While I'm feeling 98 per cent okay, I know I'm still not quite right," said Jacobson. "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 said 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.