New Zealand captain Kane Williamson was still mulling over the make-up of his side ahead of Saturday's third test against South Africa with the Seddon Park wicket proving difficult to pin down.

Pace bowling duo Trent Boult and Tim Southee have been ruled out of the match with the uncapped Scott Kuggeleijn brought into the 13 to provide cover, with Matt Henry and Neil Wagner expected to start.

Williamson also suggested the hosts could consider picking two spinners in Mitchell Santner and Jeetan Patel, with just one all-rounder from Jimmy Neesham and Colin de Grandhomme.

"It's an interesting process, with so many injuries, to try and nut down the balance we want to go with," Williamson told reporters in Hamilton on Friday.

"It (the wicket) never has a huge amount of pace but offers a little bit for the seamers, and I think that side of the block can be a little slower than the other side.

"So there might be a little spin."

Williamson was unsure as to whether uncapped all-rounder Scott Kuggeleijn would make the side, but said he had been impressed by his performances in first-class cricket.

Kuggeleijn has captured 166 first class wickets in 51 games and averages almost 31 with the bat.

"He's an exciting prospect, been playing very well for a number of years at domestic level," Williamson added.

"He's been one of the top performers with the ball in hand but has also scored a number of runs in that middle to lower order.

"It's exciting for him to be involved."

South Africa lead the three-match series 1-0 after an eight-wicket victory in the second game at the Basin Reserve.

Boult and Southee were not the only absentees for the last match in New Zealand's domestic programme, with senior batsman Ross Taylor also out injured.

The hosts collapsed against South Africa in the second test, with Keshav Maharaj taking career-best figures of 6-40 on a pitch that was not offering much assistance to the left-arm spinner.

Williamson said his team have to play better in Hamilton.

"There's a number of young guys in the team and they're really looking forward to the challenge of playing one of the best teams in world cricket," he said.

"We want to go out, show some fight, play a few shots, bowl in the right areas, be nice and aggressive and leave it all out on the field."