Ireland will be without inside centre Robbie Henshaw and fly-half Jonathan Sexton for their final November international against Australia.
Henshaw was knocked unconscious by a shoulder contact to his jaw last week, suffering a concussion, and will not be involved on Saturday.
In an update from Irish team manager Mick Kearney he added that Sexton suffered a minor hamstring injury and has been ruled out this week.
Further concern surrounds blindside flanker CJ Stander, who was removed against New Zealand for a suspected concussion and will complete the HIA process and the return to play protocols, and full-back Rob Kearney after he developed concussive symptoms after the clash.
Ireland are sweating over the fitness of tighthead prop Tadhg Furlong (dead leg) and wing Simon Zebo.
Ulster centre Stuart Olding and Munster centre Rory Scannell have been added to the squad to provide additional cover, with Ultan Dillane, Peter O'Mahony and Keith Earls all set to return to the training field this week ahead of the mouth-watering Test match with the Wallabies.