Ireland coach Eddie O'Sullivan believes his Grand Slam-chasing team will face an element of the unknown when they tackle France in Dublin.
Les Bleus must win at Lansdowne Road to have any chance of retaining the RBS 6 Nations title following their 24-18 home defeat against Ireland's main championship rivals Wales.
And O'Sullivan is at a loss to know how the French will respond as this season's tournament races headlong towards a thrilling climax.
"France were shell-shocked at the end of their game against Wales," he said, after masterminding Ireland's 19-13 victory over England which sent the world champions spinning to a third successive RBS 6 Nations defeat and into wooden spoon contention.
"They (France) would have thought at half-time they were going to win that game by 20 points, but you have to give credit to Wales because I don't know many teams who would have sustained that sort of pressure and survived.
"It was a phenomenal defensive performance, and when Wales got the breaks they shell-shocked France by taking two tries.
"I am not sure what that will do for France," he added. "Will France come to Dublin with a
different team? Will they come to Dublin more galvanised by losing that game? One thing we do know is that we have to be ready to play them.
"They showed phenomenal skill and power against Wales. They have incredible pace in the backs, who are very big strong men. It is another day's work that has to be done, but
we are looking forward to it."
As head coach Stuart Lancaster polishes the axe he will soon wield over his World Cup training squad, Exeter Chiefs coach Rob Baxter has backed Jack Nowell, Henry Slade and Luke Cowan-Dickie to be given a stay of execution.
Italy Under-20s held off a late Samoa blitz to retain their place in the World Rugby U20 Championship on Saturday and head coach Alessandro Troncon believes the experience will have served as a valuable lesson for his young troops.