Conor Murray has been ruled out of Ireland's Test against world champions New Zealand this weekend, the Irish Rugby Football Union announced on Monday.
The British and Irish Lions scrumhalf has not played since injuring his neck during Ireland's tour of Australia in June.
Nevertheless, Ireland coach Joe Schmidt said following last weekend's 28-17 win at home to Argentina that Murray, one of the world's leading scrum-halves, could still make a shock return against the All Blacks at Dublin's Lansdowne Road on Saturday.
New Zealand coach Steve Hansen said on his team's arrival into Dublin that he expected Murray to play this weekend, despite his long absence.
But the IRFU confirmed on Monday that Murray, who was omitted from reigning Six Nations champions Ireland's original November internationals squad, would not feature at all this month.
"Conor Murray is accelerating through his recovery but will not join the squad during the Guinness Series window," their statement said.
Ireland centre Robbie Henshaw will also miss the Tests with New Zealand and the United States after suffering a hamstring strain while warming-up shortly before kick-off against the Pumas last Saturday.
"Robbie Henshaw's hamstring issue will rule him out of the remainder of the Guinness Series," the IRFU added.
Jonathan Sexton, with whom Murray has formed one of the most feared half-back partnerships in Test rugby, said the Munster star had made the right call.
"It's probably a smart thing," said Sexton.
"It's a big ask. If you're out for a few weeks and you're asked to play the All Blacks, that's tough enough.
"But if you're out for the period of time he has been out for, it would be a big step in."
Sexton, who along with Murray was pivotal in the Irish securing last season's Six Nations Grand Slam, backed whoever from Kieran Marmion or his Leinster team-mate Luke McGrath started at scrum-half.
"Look, he's a world-class player and three guys behind him are chasing him but I think they did well at the weekend, 'Marms' and Luke," said Sexton.
"They'll be better for that experience as well. I think the more time you spend in the environment in here, the more comfortable you get and the better you get.
"I'm sure those guys will go a step ahead again this week."
Ireland had already lost flanker Sean O'Brien for the All Blacks clash and suffered another blow on Monday.
Centre Robbie Henshaw will also miss the duel between the two top ranked teams in the world -- as well as the United States match a week on Saturday -- after suffering a hamstring strain while warming-up shortly before kick-off against the Pumas last Saturday.
Sexton said his loss would be felt.
"Yeah, Robbie has been a big part of the team over the last number of years," said Sexton.
"Look, I'm sure he'll bounce back quickly from it but he's obviously a loss.
"He'd be a loss for a lot of teams in the world and he'll be a loss for us this week."
Ireland takes on New Zealad in Dublin on Saturday November 17, kicking off at 7pm local, Sunday 6am AEDT, LIVE on beIn Sports, Foxtel channel 515