Tim Southee's withdrawal from the third test squad sharpens the selection possibilities for New Zealand in the final test of the summer against South Africa.

The senior seamer is out with a grade one hamstring tear picked up in the second test loss in Wellington. No replacement has been named.

That means a couple of things: New Zealand have a like-for-like replacement in the group in Canterbury's Matt Henry; but also that they may already have decided on a two-seam, two-spin bowling mix for Seddon Park, where the test starts tomorrow, weather permitting.

Therefore there's no need to bring in a further player, who won't be playing in any case.

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The absence of Southee is a blow. It means that out of seven tests at home - and assuming swing man Trent Boult is fit to play after missing Wellington with an upper leg injury - and a possible 14 appearances by Southee and Boult, they have been restricted to just 10.

Southee was omitted for the first test against South Africa in Dunedin, and misses Hamilton; Boult was out injured for the second Pakistan test in Hamilton in November and missed Wellington.

Their figures have been outstanding in the home summer - Southee 29 wickets at 22.5 each; Boult 22 at 22.5.

The third regular fast-medium wheel, Neil Wagner, has taken 28 at 25.14 apiece, and has been there for all seven tests, assuming he's picked for tomorrow.

There seem three options for New Zealand for tomorrow: pick Henry and give New Zealand three seamers, one spinner and a couple of medium pace helpers in Colin de Grandhomme and Jimmy Neesham; introduce left arm spinner Mitchell Santner, giving New Zealand two frontline seamers and two spinners, Santner alongside Jeetan Patel; or leave Henry on the sideline and take the same bowling make-up as they had in Wellington, with Boult in Southee's spot.

That presupposes Boult is passed fit. If not, start the computations again.

Meanwhile, opener Jeet Raval is backing fellow leftie Tom Latham to come right.

The Canterbury opener has struggled, with just 33 runs from his last eight international innings.

Raval, who has hit four half centuries in his first six tests and is averaging 40.5, pointed out all batsmen have a lean trot but is sure Latham will get out of the hole.

"Tommy's going to come right. He is a world class player, and been a massive member in this group for a long period of time," Raval said.

"He's working as hard as anyone, and I sure he's going to come good."

Raval's recipe for getting out of a slump?

"It's about understanding what has to be done, going back to basics and doing as well as you can.

"If you're willing to spend time in the middle, it will eventually turn around for you."