Veteran Ireland centre Garry Ringrose is set to miss all of next month's Nations Championship fixtures in Dublin because of a hamstring injury.
An Irish Rugby Football Union (IRFU) statement issued on Tuesday said the 31-year-old Leinster star would continue his rehabilitation with provincial side Leinster.
"Garry Ringrose (hamstring) is unlikely to be involved in the forthcoming matches against Argentina, Fiji and South Africa in Dublin and will continue his rehabilitation with Leinster," the IRFU said.
Ringrose -- who was first capped in 2016 and has been a pivotal figure in Ireland's Six Nations Grand Slams (2018/2023) -- joins other key figures including captain Caelan Doris and flyhalf Jack Crowley in missing the November tests.
Andy Farrell's squad has assembled in Dublin ahead of their game against the Pumas at Lansdowne Road on November 6.
Flyhalf Sam Prendergast will continue his rehabilitation from a wrist injury in camp. Utility back Jimmy O'Brien sustained a concussion at the weekend and aims to resume full training later this week.
Ireland beat Australia and Japan in the southern hemisphere leg of the competition in July before losing to New Zealand.
Following next month's opener against Argentina, Ireland face Fiji on November 14 before hosting world champions Springboks a week later.
The Nations Championship is designed to provide an extra competitive edge to the July and November international windows.
It culminates in a finals weekend at Twickenham from November 27 to 29, where northern and southern hemisphere teams will be matched according to their respective rankings, with an overall winner crowned.