New Zealand's worst spin bowling fears have materialised. Left-arm spin bowling genius Daniel Vettori has a stress crack fracture in his back.

He will not play in South Africa with the CLEAR Black Caps after the ICC KnockOut tournament in Kenya.

Vettori, 21 and the youngest spinner in Test cricket to take 100 wickets, told CricInfo earlier this week that he hoped to be recovered in time for the South African leg of the season.

However, he is now looking to New Zealand's one-off Boxing Day test against Zimbabwe as his return to international play.

"I'm targeting being back for the Boxing Day Test against Zimbabwe at the Basin Reserve. In the meantime, I'll be engaged in a programme of light build-up such as swimming for the next month and then if all goes well, the medical team will be getting me to take on a heavier build-up so that I will be ready in December," Vettori said.

Vettori has had several scans of his back in Christchurch this week as experts sought the cause of the pain that forced him out of the first test against Zimbabwe in Bulawayo.

The head of New Zealand Cricket's medical panel, Dr Rob Campbell said the tests revealed a crack in one of his bones.

It was not as serious as a fracture, he said, but would require careful rehabilitation.

"Before he went away last month, he was fully recovered, was symptom-free and was able to cope with a full bowling workload.

"It was just one of those things that Daniel now appears to have a cracked bone in his back, which was not there when he was fully examined after his back problems in March.

"We will now look at all aspects of his bowling action and physical training regime in order to see what is causing the problem.

"Fortunately, we have every confidence that given the right rehabilitation programme, he will fully recover and we expect him to be back in top cricket before too long, Dr Campbell said.

New Zealand Cricket (NZC) operations manager John Reid said the back injury outbreak which has also slowed Geoff Allott and Dion Nash has resulted in a special meeting being arranged of NZC's medical panel to review the coaching, conditioning and workload demands for bowlers.

© CricInfo