The Irish have selected an experimental side for the non-cap international at Thomond Park with only Jamie Heaslip, Conor Murray and Mike Ross surviving last weekend's defeat by South Africa.
Instead, the likes of uncapped Ulster trio Luke Marshall, Craig Gilroy and Paddy Jackson have been given a chance to impress the management.
"Fijians are renowned for how aggressive and physical they are," said Leinster winger McFadden.
"They have massive men across the board - throughout the backs and in the forwards.
"They'll be physically opposing, but we'll be up for it because a lot of our lads didn't get that much game time last week.
"We'll be looking to come out of the blocks fast and impose our gameplan on them.
"We want to put some structure on the game. Fiji feed off scraps and thrive on loose ball."
McFadden is the most experienced member of Ireland's backline with 15 caps and he is excited by the prospect of linking up with the new arrivals.
"I've played with Darren Cave all the way through under-age, I've known him for years," he said.
"Luke has slotted in very well and Paddy Jackson has an old head on young shoulders. Those lads are very promising, hopefully they'll go well."
Due to the non-cap status of tomorrow's clash in Limerick, Ireland have been denied the chance to end their five-Test losing sequence.
They succumbed 16-12 to South Africa last Saturday in a match they should have won and conclude their autumn against Argentina in eight days.
"The mood's been great, we've been flying, but getting pipped by South Africa was a disappointment," McFadden said.
"It was a good team performance. They strangled out the latter part of the game by not giving us any scores.
"But some fresh faces have been brought in and they're really looking forward to it. Hopefully we can put things right."
Second row Mike McCarthy was called up to the bench this morning after substitute Donnacha Ryan withdrew from the 23 due to illness.