Speaking to the Daily Mail Luatua revealed joining English club Bristol last year was incredibly difficult, mainly because of his ambitions to play for the All Blacks in the British and Irish Lions tour.
Luatua wasn't selected for the All Blacks during the tour because of his new signing despite being a standout performer in the back row.
"Giving up the All Blacks jersey, especially ahead of the Lions tour, was the hardest part," Luatua said.
"I do have ambitions to play at a World Cup, maybe in 2023."
The former Blues flanker joined the English Championship side in the back half of last year on a two-year deal.
Luatua played 15 Tests for the All Blacks from 2013-16 but didn't feature at the Rugby World Cup in 2015.
New Zealand Rugby rules stipulate a player must be playing in New Zealand to be eligible to play for the All Blacks.
Bristol were relegated from the English Premiership to Championship at the end of 2017 but are unbeaten in 13 games this season under head coach Pat Lam.