"It's fairly disappointing because I've had a fair amount of time racing triathlon and I believe that performing in a race is quite different to just being able to produce a time during a training session.
"I just think it's unfair. Why don't they talk to my coach or just look at race results or performances and just pick teams off that? It's become a very different selection and something I disagree with quite strongly.
"Triathlon New Zealand knew exactly what I was doing but I don't feel they're very supportive of what I've been doing. They've made it very difficult for me, but I'm not doing the sport for them, I'm doing the sport for me. I decided this was what was best for me. It is unfortunate they do not have the same viewpoint."
However, TNZ high performance boss Mark Elliott says their decisions are performance-based and at the moment they prefer Sam Ward and Taylor Reid over Sissons.
"I wouldn't say he's not good enough. It's just that the other guys have performed exceptionally well. It's a pretty tough call," Elliott told Radio Sport.
"It's not about athletes being good enough, it's actually about who's best for the structure of the team at the moment. And at the moment with that strong swim and bike capability of Taylor, and Sam's exceptional circumstances and what he's doing at the world stage at the moment - he's also swimming to another level at the moment as well."
Elliott denied Sissons' claim that his snub was solely due to his change in training.
"It doesn't matter where he's training if Ryan was racing and showing the performances that we've got from those other boys then obviously we have to take that into consideration.
"He's saying what he's said, at the moment we're focusing on what's best for the team and who those athletes are and at the moment, Sam and Taylor are doing some exceptional stuff.
"And I'm sure Ryan will be there in the future and let's hope his racing keeps on improving and putting himself in a position to be considered as well."
Meanwhile, Elliott also confirmed Olympian Andrea Hewitt was left out of the team relay of the world championships event at her own request because of illness.
"Unfortunately Andrea had a medical. She hadn't been feeling too well, she had a stomach bug a week before.
"She felt that for herself, she wasn't going to be 100 per cent and if she couldn't deliver a 100 per cent to the team she felt that [pulling out] would be a better option for us."