Toulon announced on Friday that the 23-year-old, a key member of the Pumas in last year's Rugby Championship and Jaguares in their Super Rugby debut season, was returning to the club for the next two northern hemisphere seasons.
Isa's decision means he will rescind his contract with the Jaguares and make himself unavailable to the Pumas given Argentina's policy of only picking European-based players for World Cups.
"Facundo Isa returns to RCT (Toulon Rugby Club)... Another big coup by RCT and its president Mourad Boudjellal on the transfer market," Toulon said on their.
Isa played for Toulon as a 20-year-old in the 2013-14 season before returning home to play for the Pampas, the Pumas' feeder team, and Jaguares.
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He helped Argentina reach the 2015 World Cup semi-finals.
(Reporting by Rex Gowar, editing by Ed Osmond)
