In a move that could possibly affect his All Black selection chances for the tournament in France in September and October, the 23-year-old has confirmed he's signed an 18-month contract with French Top 14 club Toulon.
He'll join the side after the culmination of the World Cup.
Fainga'anuku said the move away from New Zealand "ticked a lot of boxes for me both on and off the field".
"I feel like I've achieved a lot playing in New Zealand, and I cherish those accomplishments as some of the proudest moments in my life so far," Fainga'anuku said.
