Hansen is stepping down as All Blacks head coach after the 2019 Rugby World Cup, and Barrett believes the 59-year-old has set a standard that will be hard to emulate.
"He'll be a huge loss – but it leaves an opportunity for someone else to step up. He's done a lot for me and my game and I have to thank him for that.
"I could only wish him the best. He's had a fantastic career and obviously the job's not done yet – we all want to win the World Cup, retain the Bledisloe [Cup] and all the rest of it."
Barrett believes that Hansen's communication and personal skills puts the All Blacks mentor a cut above the rest of the world's top coaches.
"His ability to understand the player and get the best out of the player [is vital]. He knows how every individual in the team ticks, he treats everyone as an individual and I think the way he's developed that, from when I first made the team to now – it's obviously been a work-on and that's why he's the best coach in my opinion.
"It's reassuring to know that your head coach goes out to bat for you when perhaps things haven't gone our way – he has our best interests at heart and he backs us 100%."
Barrett was speaking at the ASB Classic, where he and All Blacks teammate Damian McKenzie competed against fourth seed and world No 23 Pablo Carreno Busta in a flute pouring competition while taking a break from watching the tennis.
Just like he does on the field, Barrett showed his usual handiwork, completing the challenge just ahead of Carreno Busta, while McKenzie was a distant third.
The experience was part of a summer of relaxation for the Hurricanes playmaker, with Barrett revealing that Hansen advised all the All Blacks to relax in advance of the hectic season ahead.
"[He said] 'make sure you really freshen up', because it's going to be a big year. Get around your loved ones, friends and family and really switch off, because come February it's all go."
The World Cup looms as the ultimate prize for the two-time defending champion All Blacks, and Barrett says the lure of raising the Cup aloft once more is always on his mind.
"I think about it every day," said Barrett.
"It just naturally pops into my mind every now and then, especially when you're training. When you train, you train for a reason, and ultimately that's a big goal of mine at the end of the season and something we're all working towards.
"Obviously there were a few results we weren't too pleased about but at least it gave us a good idea of where we need to be."