Liam Squire says he didn't feel "physically or mentally" ready for the pressures of a Rugby World Cup.
The 23-test All Black was left out of coach Steve Hansen's 31-man squad for the tournament - the selectors opted for the inexperienced, but talented Luke Jacobson.
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On Squire's omission, Hansen commented that the two had a productive phone call, but reached the agreement that Squire should continue shining for Tasman and be ready for a call if the injury bug strikes in Japan.
The loose forward had an injury-ravaged Super Rugby campaign, then opted out of the All Blacks Rugby Championship squad citing form and personal reasons.
Squire released a statement on social media late Thursday explaining the reasons for his absence from the national side.
"After what has been a really tough year for me mentally and physically, and after speaking with people I trust on whether I should make myself available again for the All Blacks, I felt I wasn't ready just yet physically or mentally for the pressures of test match rugby," Squire wrote on Instagram.
"I feel I need to earn the right to pull on the Black jersey again through performing well for my beloved Tasman Mako and keep ticking the boxes there.
"As Steve said yesterday, if the All Blacks do get injuries, and I'm performing well enough, then I'm 100% available. The decision has been bloody hard but I feel it's the best one for me and the All Blacks. I wish the team every success and am behind them 100%.
"I have never been one to speak a lot publicly so I hope people can respect my privacy and decision on this and I can move forward and keep enjoying my rugby.
"For me mental health is a lot more important than playing rugby."
Squire's form for Tasman in the early stages of the Mitre 10 Cup opened eyes around the country, and as late as 48 hours before Hansen and his selectors revealed their squad, reports surfaced the 28-year-old was ready to recommit to the All Blacks.
His phone call to Hansen earlier this week may not have produced the result some rugby punters had hoped for, but Squire may still have a role to play in Japan in the coming months.