"We think that [Neesham's] got something a little bit special, and obviously with Kane under a bit of a cloud with his bowling and the legitimacy of that at the moment, we still need to create a bowling option in that top five," McCullum said, before praising the rapidly evolving venue.
"I guess it's a sign of the times when grounds like this are getting an opportunity. It looks fantastic, the ground looks amazing, especially for this time of year, and the pitch looks really good too, so the boys are looking forward to playing against a top international team so early in the season."
An interesting sideshow to proceedings was the appearance of Williamson at the bowling crease of the Bay Oval grass nets.
The 24-year-old, who was banned from bowling in international cricket in June following biomechanical testing, was trying out various kinds of tweakers with some impressive results.
The left-arm off-spin looked surprisingly effective but it was the distinctly different right-arm off-spin, featuring an altered run up and loading position and, most importantly, a far straighter, higher arm action that hinted his return to the bowling crease may not be too far away.
The New Zealand captain was impressed with the evident changes to Williamson's action, comparing the young Northern Districts player's action front on to former England spinner Graeme Swan.
"I don't quite know about the testing side of it but, just from looking at his action ... front on facing him, I thought he's definitely worked out his problem.
"That was really encouraging to see that. He's such a talent he can make subtle adjustments to his game as well - we've seen that with his batting. To me, he doesn't look too far away, so it will be interesting to see what happens when he gets tested."
The captain did not know the timeline for any future testing but joked sometime before next year's World Cup would be handy.
View a video of Black Caps captain Brendon McCullum and Proteas caption AB de Villiers below, or mobile and app users click here.
ODI squads
New Zealand: Brendon McCullum (c), Corey Anderson, Trent Boult, Dean Brownlie, Martin Guptill, Matt Henry, Tom Latham, Mitchell McClenaghan, Nathan McCullum, Kyle Mills, James Neesham, Luke Ronchi, Tim Southee, Daniel Vettori.
South Africa: AB de Villiers (c), Kyle Abbott, Hashim Amla, Quinton de Kock, Jean-Paul Duminy, Faf du Plessis, Ryan McLaren, David Miller, Morne Morkel, Wayne Parnell, Aaron Phangiso, Vernon Philander, Rilee Rossouw, Dale Steyn, Imran Tahir.
