Ireland must shut down Sevens star Virimi Vakatawa at source to pull off back-to-back victories in France for the first time in 89 years, according to Dave Kearney.
Wing Kearney could slot into Ireland's starting line-up in Paris on Saturday if Keith Earls fails to prove his fitness after suffering a suspected concussion against Wales.
Vakatawa's try-scoring Test debut in France's 23-21 win over Italy last weekend was the Fiji-born flyer's first 15-a-side match in almost three years.
Ireland will chase two wins on the spin in Paris for the first time since 1927 in Saturday's RBS 6 Nations encounter, but Kearney has sounded the latest warning on France's newest attacking menace.
"You know that he's got real threats from the fact he's thrived in Sevens," said Kearney, of Vakatawa.
"Give someone like that space and they cause you trouble.
"He'll be looking for the space and he'll be wanting to exploit any gaps.
"And he'll be wanting to use his footwork to cause problems."
Vakatawa's fine sporting pedigree stems from attending Fiji's Lelean Memorial School, the same rugby nursery as such luminaries as Sevens great Waisale Serevi.
France-based Fiji star Sireli Bobo convinced Vakatawa to join Racing 92 in 2010, and the raw talent scored on his Heineken Cup debut - a 36-11 pool-stage defeat to Joe Schmidt's Leinster in January 2011.
Now 23 and honing in on the Rio Olympics with France's Sevens side, Vakatawa could yet join triple European champions Toulon next season.
Les Bleus' venerated new head coach Guy Noves, who guided Toulouse to four Heineken Cup titles, has vowed to restore France's traditional free-flowing attacking verve - and Vakatawa fits that bill.
Leinster wing Kearney admitted the only way to stop a quick-witted backline talent like Vakatawa was to deny him any room to manoeuvre.
"You've just got to get into him and get up as quick as you can," said Kearney.
"Depending on what happens and how we play defensively, but hopefully we'll know the threats of those guys around the edges.
"We know that all their wide players can be devastating if given the opportunities."
Head coach Joe Schmidt has admitted Ireland must adapt their defensive strategy to secure another victory over France on Saturday.
The Ireland boss accepted his side can ill afford to take the kind of gamble without the ball against France that paid off in Sunday's tense draw with Wales in Dublin.
Kiwi boss Schmidt was happy to try to squeeze Wales' naturally-direct attack last weekend, but has warned the French will punish any repeat without mercy.
"I did get a good look and we can't afford to be quite so narrow defensively against France," said Schmidt.
"You can get away with that against Wales but it's real risk against the French, the width they played with was pretty impressive at times.
"And I think you're just going to have to be careful no matter what you do.
"So we're going to have to make sure we're very clinical with the ball, and try not to allow them too many opportunities."