Ireland second-row Iain Henderson will miss the Six Nations clash with Wales after suffering a hamstring injury, while captain Caelan Doris could also be sidelined for the showdown in Cardiff.
Henderson and fellow Ulster lock forward Cormac Izuchukwu, who has an ankle problem, will both be absent on Saturday as Ireland seek to win the Triple Crown after victories over England and Scotland.
Henderson played as a replacement in the tournament opener against England but was absent for the victory in Edinburgh.
Doris, who has been outstanding at No 8, is in a race against time to be fit after sustaining a knee injury against Scotland in Edinburgh.
"Gavin Coombes, John Hodnett, Diarmuid Mangan, Stuart McCloskey, Jacob Stockdale and Nick Timoney have all been added to the squad, with Iain Henderson (hamstring) and Cormac Izuchukwu (ankle) unavailable due to injury," said an Ireland squad update published on Sunday.
"The Ulster duo will remain with their province to recover and commence their rehabilitation programmes.
"The workloads of Caelan Doris (knee) and Ronan Kelleher (neck) are being managed this week.
"Tadhg Furlong is continuing to make progress and both Mack Hansen and Joe McCarthy are back training with the squad."
Ireland interim boss Simon Easterby will name his squad to play Wales on Thursday.