"It's important we give all squad members an opportunity to perform and certainly there will be players who will be performing a role in these matches that they'll be expected to do at World Cup time."
McMillan said although Southee was resting a slight hamstring issue, "you'll find most have niggles".
"It's part and parcel of being a professional cricketer.
"There's very few players at bang on 100 per cent. It's about maintenance".
It is expected Tom Latham or Grant Elliott will be sharing No 5 duties, in captain Brendon McCullum's former role.
As for the skipper, who is back at the top of the order - alongside Martin Guptill, with whom he has a good opening record - a glance at the statistics might give him an extra jab of incentive. While he averages 33 in all ODIs, McCullum is going at a less than ordinary 17 in 23 matches against the Sri Lankans.
Given that New Zealand face the Sri Lankans in the cup opener, and doubtless desperate to get their campaign off on the right foot, they are unlikely to show all the cards in this series.
However, McMillan has a slightly different take.
"All 15 will get game time but it's important to win, and from that point of view we won't be trying too much"
The New Zealand players will be watched closely in pressure situations over the next few weeks. Trying to mimic what might happen at the crunch time in the cup is all part of the preparation.
Sri Lanka are bolstered by champion batsman Mahela Jayawardene, who retires from international cricket after the cup, dashing opener Tillekaratne Dilshan and big-hitting allrounder Thisara Perera for the series.
Star seamer Lasith Malinga, getting over ankle surgery, is unlikely to be sighted before at least game four of the rubber in Nelson on January 20.
Sri Lanka are a formidable one-day outfit, invariably fighting hard at the sharp end of big events. New Zealand should get a quality workout.
However, while seven ODIs against Sri Lanka, then two more against Pakistan at the end of this month is a solid run-in, if you were to tailor your leadup, fewer games against one team and perhaps three against another side might be preferable.
The schedule means there can be no excuses for getting caught short on February 14.
NZ v Sri Lanka
First ODI
Christchurch, 11am tomorrow
New Zealand: (from) Brendon McCullum (c), Martin Guptill, Kane Williamson, Corey Anderson, Tom Latham, Grant Elliott, Luke Ronchi, Dan Vettori, Nathan McCullum, Mitch McClenaghan, Adam Milne, Trent Boult.
Sri Lanka: (from) Angelo Mathews (c), Tillekaratne Dilshan, Dimuth Karunaratne, Kumar Sangakkara, Mahela Jayawardene, Dinesh Chandimal, Lahiru Thirimanne, Thisara Perera, Nuwan Kulasekara, Jeevan Mendis, Rangana Herath, Suranga Lakmal, Sachithra Senanayake, Dhammika Prasad, Shaminda Eranga.
NZ v Sri Lanka ODI record
Overall: P 82, won 38, lost 37, tied 1, N/R 6
In New Zealand: P27, won 17, lost 9, N/R 1.
