New Zealand's left arm swing bowler Trent Boult is out of the second test against South Africa, starting at the Basin Reserve tomorrow.

Boult has picked up an injury to his upper left leg and took no part in training today. He's expected to head home to Tauranga for some rehabilitation later today.

No decision has been made on his replacement, but senior seamer Tim Southee is sure to return after being dropped for the first test in Dunedin to allow New Zealand to field two specialist spinners.

Canterbury seamer Matt Henry is the leading candidate to come in and form a three-pronged seam attack with Southee and left armer Neil Wagner, while two spinners at the Basin is extremely unlikely.

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That means one of left armer Mitchell Santner or veteran offspinner Jeetan Patel will sit the test out.

Patel has never played a test on his home ground but there were signs that may change tomorrow. The Wellington man spent time on his own beside the test pitch bowling at a stump, as if visualising how things might pan out tomorrow.

Batsman Neil Broom has been confirmed to replace Ross Taylor for his debut test at No 4 in the order.

Southee will miss his regular new ball partner Boult, but said he was simply not right to play in the test.

"Not probably (well) enough to go again with another heavy workload possible here so unfortunately he's going to miss this one," Southee said of Boult.

It is the second test at home this summer that Boult has missed.

He sat out the second test win over Pakistan at Hamilton in November due to a knee injury.

This would have been his 51st test. He's taken 190 wickets at 28.7 and is ranked 13th in the test bowling list.

Southee knows what it's like to miss a test, after Dunedin.

"Obviously there were a range of emotions that went through but at the end of the day you've got to respect the decision," he said today.

"They're only doing what they think best for that game. You've just got to get on with it and work hard and try to help the other guys for the test."

Among the decisions still to be taken is whether New Zealand will field a second specialist spinner. It seems highly unlikely but there was no confirmed word on that today.

If selected, Patel, 36, would be playing his fourth test out of the last eight by New Zealand since his recall after a three-and-a-half year absence from the national team on the tour of India late last year.

He's taken 62 test wickets at an ordinary 47.88 apiece but he has seemed more likely to take wickets than Santner, who is seen as a drier operator.

Patel also took four wickets to Santner's one in the first test at Dunedin, and was used for 69 overs compared to 37 by the left armer.