The match is do or die for both teams - defeat would send France crashing to a humiliating group exit while Ireland, who finish the pool against Argentina, believe it is their pivotal contest.
With the stakes so high, Ireland coach Eddie O'Sullivan has taken a gamble on 26-year-old Reddan - and Easterby believes it could prove a masterstroke.
"There's no desperation in the team selection," said the Ireland blindside.
"Eoin Reddan deserves his chance because he has been playing well for Wasps.
"He will add a different dimension to what Peter brings. He has played for Ireland before so I don't think it's a risk.
"It's not an issue. France haven't seen as much of Eoin as they have of Peter and that may work in our favour.
"It will put doubt in their minds over what he will bring to the game."
A slow start from the pack has marred Ireland's opening two games against Namibia and Georgia and a vast improvement will be needed if they are to compete with the French forwards.
But Llanelli back row Easterby believes the resistance his side showed up front during Saturday's 14-10 victory over the Georgians stands them in good stead.
"I thought the pack performed well against a strong Georgian side. They are a very physical team," he said.
"The scrum was OK, the lineout was very good. OK, they managed to get the rolling maul going but they didn't score a try from that.
"We're happy with the way we played against Georgia. When the Georgians pull that jersey on they play pretty well.
"We have some improvement to make and hopefully we'll see that against Georgia."
Ireland's build-up to the match has been the most troubled in recent memory, with angst over selection and discontent at the location of the team hotel contributing to the gloomy atmosphere that has descended on the camp.
But victory over France, who are 1-7 to triumph in Paris on Friday, would provide the squad with a huge lift and Easterby is refusing to raise the white flag.
"We know we must perform better than we have been, but we also know we're capable of doing exactly that," he said.
"It's our biggest Test match for a long time and we don't need any extra motivation.
"We've been written off by the press but hopefully we'll see a good performance on Friday."