Ireland's first-choice fly-half, Jonny Sexton, is a serious doubt to play in Sunday's quarter-final against Argentina according to his team's assistant coach Les Kiss.
Sexton limped off after 25 minutes in Ireland's hard-fought 24-9 victory over France last Sunday.
The result saw Ireland finish top of pool D and they managed to avoid a last-eight clash against defending champions New Zealand.
"Jonny has a slight adductor strain," explained Kiss.
"There's been some improvement. Hopefully we'll see a little bit more on Wednesday and that'll give us a clearer picture.
"Each day will give us some more information."
Although Sexton might not be available for Sunday's clash Ireland can fall back on Madigan, who showed his class after replacing Sexton against France.
"He's slotted in seamlessly," said Kiss of 26-year-old Madigan.
"He's armed, he's ready, if it has to be the case he'll step forward."
However, the loss of skipper Paul O'Connell, flank Peter O'Mahony and centre Jared Payne to injury is a big blow for the men in green.
"He is the brains behind a lot of the forward game," said Toner of O'Connell.
"For the team it's a massive loss.
"But it's happened before that we've lost players for games, that we've had to dig deep in our squad, and we have confidence in our squad these days to pull through.
"We've worked hard to forge that strength in depth and forge that strength in the squad and being able to do that the way we did (against France) was hugely positive and we can take that into the next game."
Kiss expects Sunday's clash against Argentina to be Ireland's toughest battle yet.
"We know it's going to be physical, we expect that without a doubt, but the thing they do show is a lot of skill," he added.
"If they play (Nicolas) Sanchez and (Juan Martin) Hernandez at 12, that is a great opportunity to play off first and second receiver and unleash (Santiago) Cordero or (Juan) Imhoff or (Joan) Tuculet. The type of the damage they can do on the edges can hurt you for sure.
"It's a really broad challenge for us.
"We've got a lot of respect for them."
Argentina have excelled in their attacking game and Toner emphasised that the new found form of the Argentinean backline was directly related to playing in the Rugby Championship alongside Australia, New Zealand and South Africa.
"I'm not surprised, no, because they're getting so much experience these days with the new competitions they have, they're getting so much more experience in big Tests," added the 29-year-old.
"You can see how well they did against the All Blacks, they played really well against them," the lock said in reference to the Pumas' 26-16 opening Pool C defeat by the defending champions.
"They've scored 22 tries so far. They're a really dogged team, they mix their physicality with their speed and I can't say it enough, they're dangerous and we're going to have to be on our toes. They've got quality all over the field."