Leinster centre McFadden will partner club-mate Gordon D'Arcy in midfield with David Kearney called up to the replacements for the game at the Aviva Stadium.
And Ireland manager Michael Kearney admitted he wasn't sure when Earls would be returning to the camp.
"The nature of the illness is unclear, however I did speak to Keith this morning and he was hopeful and optimistic that the baby would get home some time over the weekend," he said.
"The decision was taken following a conversation with [head coach] Declan [Kidney] and Keith yesterday and it was thought that it was in the best interests of Keith and his partner Edel and their families that Keith remains in Limerick for the weekend."
Meanwhile wing Andrew Trimble insists Paul O'Connell will more than make up for the absence of O'Driscoll after taking over the captaincy.
"There are different types of leader out there and O'Connell is someone I have a massive amount of respect for," he said.
"When he speaks, everyone else listens. That's the way it is with Paul.
"Captaincy is still massively important. At Ulster we have Johann Muller and Rory Best. They make the decisions and do the talking.
"They're clear and concise, telling us what we need to do, and that's good leadership.
"Other leaders, such as Ruan Pienaar, do the right thing at the right time. He doesn't talk things up, just tends to make the right decision."