Despite being assured by the All Blacks coaches, Charles Piutau can't shake the feeling that his move to Ulster played a part in his World Cup omission.

Charles Piutau believes his decision to move to Europe played a part in his surprise omission from the All Blacks World Cup squad.

The 24-year-old utility was deemed the unluckiest player to miss out on Steve Hansen's 31-man group that went on to defend their crown in England earlier this month.

It came after Piutau dropped a bombshell on New Zealand Rugby (NZR) earlier this year when he agreed to a lucrative two-year-deal with Irish club Ulster for 2016. He is seeing out the season with English outfit Wasps after NZR blocked him from playing for the Blues next year.

Piutau said he was assured by Hansen that his departure was not behind his World Cup snub, although he is still not convinced that is the case.

"It's human to have those 'what ifs'," he told Britain's Daily Mail.

"I gave everything I could to be selected. I knew there was a possibility that moving could affect my chances.

"The coaches told me it wasn't the reason, but I felt it was partly. It was tough. No player likes to be a spectator in the biggest tournament.

"It was quite hard to swallow. I backed myself to make that team but it wasn't to be."

Piutau looked to have booked his ticket to the World Cup following a standout performance on the wing against the Springboks at Ellis Park in July.

But Hansen ultimately went with rookie sensation Nehe Milner-Skudder, who started in all of the knockout matches, and Waisake Naholo, despite the fact he was recovering from a broken leg.

Piutau is doing his best to put the setback behind him though, playing a starring role in his Wasps debut last week as they beat Gloucester in the English Premiership.

He gets his first taste of the European Rugby Champions Cup early Monday morning (NZ time) when Wasps take on Leinster in Dublin.