Kane Williamson will lead New Zealand in McCullum's absence. Whoever was calling the shots would have big shoes to fill. New Zealand have been without McCullum before but it's common knowledge that the time is approaching when the little man will be gone for good.
"When he's there you've got that experience of 250-plus ODIs and obviously he leads from the front," Guptill said.
"You can see by the way he bats. He takes the game by the scruff of the neck and throws himself around (in the field). The other guys really thrive off that. He gets the best out of everyone. When he's not there it's up to the rest of the guys to pick up that slack."
No Boult or Southee opens prospects for the other seamers, Mitch McClenaghan, who had a tough time in England but a successful stint in the Indian Premier League with winners Mumbai Indians, Wheeler, Adam Milne and Doug Bracewell.
"Mitchell has a very good one-day record and we'll be looking to him to set the tone with the ball and Ben's had a great start to his international career and he's got another opportunity to show his stuff and push for further selection down the track."
New Zealand have a week-long camp in Potchefstroom before playing three ODIs and a T20 against Zimbabwe, all in Harare, followed by two T20s and three ODIs against South Africa.
New Zealand squad: Kane Williamson (c), Martin Guptill, Tom Latham, George Worker, Ross Taylor, Grant Elliott, Colin Munro, Jimmy Neesham, Luke Ronchi, Nathan McCullum, Doug Bracewell (South Africa only), Ish Sodhi (Zimbabwe only), Ben Wheeler, Mitch McClenaghan, Adam Milne.