Ireland will be without Joey Carbery and Robbie Henshaw for Saturday's rugby Test match against Australia.
For the Wallabies Test the following week, Wales have already ruled out lock Will Rowlands and loose-forward Dan Lydiate.
Kiwi-born five-eighth Carbery will have to complete return to play protocols following his removal from Ireland's win against Fiji on Saturday for a head injury assessment (HIA).
Centre Henshaw, the 29-year-old British & Irish Lion, missed the 19-16 victory over the Springboks but returned for the 35-17 success over Fiji in which he suffered a recurrence of an injury.
"Robbie Henshaw's hamstring issue will rule him out of this week's game ... he will continue his rehab at Leinster," the the Irish Rugby Football Union (IRFU) said in a statement.
Fullback Jimmy O'Brien will complete the HIA process on Monday and is expected to be available to train after that.
"The players who picked up knocks against South Africa -- Johnny Sexton, James Ryan, Andrew Porter, Josh van der Flier and Hugo Keenan -- will be monitored across the early part of the week and re-integrated into training according to their individual management plans."
Lock Joe McCarthy returns to the squad having completed his return to play protocol, while Connacht centre Bundee Aki - who has trained with the squad for the last few weeks - is available for selection again having completed an eight-match suspension and the coaching intervention programme.
Players who sustained knocks against South Africa - Johnny Sexton, James Ryan, Andrew Porter, Josh Van Der Flier and Hugo Keenan - will be re-integrated as they return to fitness.
Wales' Lydiate has a broken arm after being forced off in the first half of Saturday's 20-13 victory over Argentina. Rowlands hurt his shoulder in the same match.
Coach Wayne Pivac has called up teenage Exeter Chiefs lock Dafydd Jenkins and 23-year-old second-rower Rhys Davies as cover. Both are uncapped.