The ASM Clermont Auvergne eighth-man joined Marcelo Loffreda, his coaching staff and the Argentina-based players in Biarritz, where the match will take place, and explained that the game will be difficult because the Barbarians have played together for a long time.
"Their players did not have the chance to play the Six Nations tournament, so they want to play this game," he said.
"This is their opportunity to show themselves and earn a berth in the World Cup squad."
Longo believes this is a great chance for some Pumas who did not play against Northampton Saints or Leicester Tigers in the last tour.
"(Argentina coach Marcelo) Loffreda still wants to go on testing players and we want to do things well."