New Zealand left-arm slow bowler Daniel Vettori faced a heavy day of medical examination in Christchurch today as he attempted to get to the bottom of the back injury which forced him out of the Zimbabwe tour.

He expects to know tomorrow just what the problem is and whether he can start working to achieve his immediate goal of playing in the South African series.

After bowling 52 overs in unresponsive conditions in the first innings of the first Test at Bulawayo, Vettori was forced to take no more bowling part in the match.

He was on the plane to New Zealand after the first day of the second Test and admitted to CricInfo that it was hard to watch the last stages of New Zealand's second win in the two-match series.

Vettori, who was unable to finish the season last year against Australia when he became the youngest spin bowler in Test history to take 100 wickets, described the injury as a setback.

"It is a dull ache, a constant pain," he said.

"I've always had a bit of a sore back but I could feel it just get worse and worse.

"I was really looking forward to playing again after last year. It is very frustrating," he said.

Vettori didn't think he was over-bowled. He said he felt good in the warm up games.

He had taken eight weeks off at the end of last summer to get his back right and then did a lot of strength and build-up work, including some weights. It was a gradual build-up.

"I never had any problems at all during the winter," he said.

It is now just a case of wait and see but Vettori is determined to be in South Africa for the Test series.

Although it is only three years since New Zealand was last in Zimbabwe, where Vettori made his first tour with the side and where he achieved his highest Test score of 90, he said there were obvious differences in the country.

"We heard about their problems over there all the time. You could also see that people were having to queue up for fuel for hours at a time. It has definitely gone downhill since we were last there.

"It is fascinating comparing the differences, you can't help but notice what is going on there. You read it in the papers.

"The people you meet are very unhappy and the players are not happy. They had some payment problems while we were there," he said.

As far as his bowling development is going, Vettori said he was pleased, at least, to have his 100 Test wickets behind him now. It became a distraction as he attempted to head Indian all-rounder Kapil Dev as the youngest player to achieve 100 Test wickets.

"I would have been disappointed if I had been hanging on getting it at the moment," he said.

"But I feel my bowling is going really well. You keep trying things. You have to. But they are just subtle variations.

"Ashley Ross (New Zealand's biomechanist) is the person I go to when I want to talk about my bowling. For me it is a feel thing, you know when it is going well," he said.

They get together and study some video analysis of his action.

And for the moment, it is more that video and television action that he is going to have to endure while New Zealand begins its One-Day International series against Zimbabwe and he awaits a verdict on what is causing his back problem.