New Zealand back-row forward Ardie Savea has been put into isolation at the All Blacks' training base after contracting mumps, it was announced Tuesday.
There is a mumps epidemic in New Zealand right now with record numbers of cases in Auckland in their worst outbreak since 1994.
But New Zealand assistant coach Ian Foster said no other member of the tour squad is currently stricken with the highly-contagious viral disease ahead of Saturday's match against Wales at Cardiff's Principality Stadium.
"Ardie has got a mild dose of the mumps," Foster told reporters in Cardiff on Tuesday. "He is the only one. He is in his room and has been in isolation.
"He was fully vaccinated as a kid, but he clearly has something. He has been in isolation for a few days and is recovering pretty quickly."
Foster said team medical officials believe Savea had caught mumps from New Zealand wing Rieko Ioane, who received treatment for the virus earlier on tour.
"We are not worried about it (spreading)," he added. "We have taken every precaution, but Ardie must have been in pretty close proximity to Rieko at some point.
"It has caught us on the hop a bit because it is not something you get a lot of.
"It has come out of the blue, but we are satisfied with the way the doctor reacted really quickly with Rieko, and Ardie was susceptible even though he had done everything right in the past. It is something we are taking seriously."
Meanwhile Foster said All Blacks captain Kieran Read had been spared training on Tuesday following some gruelling recent Test appearances for the No 8.
"He's pretty battered after the last couple (of games), and we took him out of training today to give him an extra 24 hours," Foster explained. "He's pretty good. He gets through a lot of work, and at this stage of the year he is just a bit sore.
"It was a management decision to pull him out today and give him a chance to walk around training and freshen up for later in the week."
New Zealand have arrived in the Welsh capital after being pushed hard by Scotland before coming through to win 22-17 at Murrayfield last weekend.
They have a formidable record of 29 successive wins against Wales, with their last defeat in the fixture back in 1953.
"It is not a matter of pulling the whole (Scotland) game apart and trying to fix everything, but fixing the critical parts we need to sort out," Foster said.
"This week we would like to start and finish a little bit better.
"It will be a very physical game (against Wales), we know that. It is about the collision area when you play Wales and the physicality."