"It's a test, there's fear and all sorts of things going through my mind but I'm looking forward to it.
"Chris was supposed to fight Shoaib Akhtar but he pulled out so I've been called in in the last minute.
"That puts me behind the eight ball a little because he's [Cairns] had about eight weeks."
Doull is putting in 90 minutes of boxing and 2.5 hours of routine training daily.
Whakatu Boxing Gym trainer David Miles, in Ngaruwahia, is his trainer.
His son, Corey Miles, a former Commonwealth Games boxer, is Doull's sparring partner.
"It's amazing for the fitness because I just can't believe the change in just a couple of weeks in getting slightly fit rather than not getting fit at all."
Doull has inherent aggressiveness, something obvious in his repertoire as an international cricketer but he now finds he has to channel it more in the ring.
"There's nerves and the fear of getting hit so training for boxing is a total body workout and I can't believe how hard it is.
"You sort of tighten around your neck and everywhere else when you're in the ring so it's a lonely place."
The sense of isolation is "way more" than when he was a Black Caps opening seamer.
"I kind of knew what I was doing on the cricket field but here I'm kind of a novice. I'm just thankful Chris is a novice as well," he says with a grin.
Combinations have emerged but his trainer has discouraged him from becoming too technical.
"He says your mind will become clustered with too many things you don't have to know."
Mateship will give way to pride and dignity.
"It's just that for six minutes on the 14th of December we're going to be enemies and neither of us like to lose so we'll have to take that attitude to the ring."
The pair's tale of the tape is pretty similar although a marginally taller Cairns tips the scale a bit more.
"I guess if you're looking at putting a contest together you couldn't have put a better one."
Doull says they will receive monetary compensation for their time away from work. Cairns runs a TV production company in Auckland.
"For the most part it's going to Kids Can."
Doull's parents, Averil and Max, of Pukekohe, died of cancer.
"So cancer research or help for cancer is a big thing for me and for this going to Kids Can is a great charity so I'm only too willing to help."
Cairns reveals he always talked his way out of school fights.
"I was never one to really use my fists."
Despite his flirtation with the sport, Cairns finds boxing very technical.
"You know it's very defence-orientated and it's just the loose combinations in training but it's also very complex."
Just clambering into the ring in the hope of knocking someone is a misguided notion.
The Canterbury ex-allrounder hasn't learned anything else about himself.
"The only thing I've discovered about myself is that I've got my health back, losing about 16 or 17kg.
"I was going to pasture a little bit as a sportsman," he says, acquiring a fighting weight that has become a yardstick for a healthy existence.
Akhtar, he says, "sort of entertained the idea but wasn't really there".
"He said to me, 'Cairnsy, look at me, look at you - there's not going to be a fight'."
"He would have been good value because he's a strong man."
Lee Parore helped Cairns on the dieting and weight-loss perspective while Monty Betham trains him.
His wife, Melanie, says not to embarrass her although their children, Isabel, 2, and 10-month-old Noah, are blissfully unaware.
"That's the message I'm getting from her so that's about as good as it gets."
His two older sons, Thomas, 11, and Bram, 10, from a previous marriage, will be watching from South Africa before they return home for Christmas.
"It'll be a no-holds barred because we'll be going out there to have the bragging rights from the commentary box.
"It won't be nice to be sitting next to the bloke who has beaten you up.
"It's good fun but we'll be taking it seriously. You can't be but ... that's our mentality."
Engaging in charity work with rail safety in New Zealand after the death of his sister, Louise, in 1993, which prompted him to establish a foundation, Cairns is delighted to help Kids Can.
"Having a high profile allows you to get behind something and give a hand to make it work."
Cairns also got his father, former cricket international Lance Cairns, involved in the fitness programme with the senior Cairns shedding about 10kg.
"He was definitely overweight and he knew he was so we've enjoyed shifting our focus health-wise."
Cairns reckons diet is a poisonous word.
"It's such a misused word. It's all about healthy choices and that's all weight loss is. It's about a healthy lifestyle."
He has parked processed foods and sugar, which got him half way there.
"You're also human and if [some things don't work out] don't beat yourself up on it," he says, often partial to a glass of wine.
"At the end of the day it's about eating food that's grown naturally and easily accessible," says Cairns.
