The visually impaired 23-year-old from Derry - double Paralympic and world champion in the T13 100 and 200 metres - announced his withdrawal after failing to recover sufficiently from a back injury at the end of the summer.

insideworldparasport had revealed last month how he was struggling to get fit in time for Christchurch.

Smyth said: "I am extremely disappointed that I am unable to compete.

"Unfortunately my training is progressing very slowly and I would not be fit enough to defend my titles

"I'd like to wish my team mates the best of luck at the Championships."

Injury also prevented Smyth from representing Northern Ireland in the Commonwealth Games in New Delhi in October.

He said: "I look forward to returning to competition in the summer and to achieving the London 2012 Paralympic qualification times at the earliest opportunity."

Smyth was heavy favourite to retain both his World Championship sprint crowns from four years ago after demonstrating his superb form earlier this year.

He reached the semi-final of the 100m at the European Athletics Championships in Barcelona where he became the first Paralympic athlete to compete at the able-bodied event.

James Nolan, head of Paralympic Athletics, said: "Jason's professional support team have been doing everything in their power to have him ready, but unfortunately the lead-in time to the championships was too short to fully rehabilitate the injury and the right decision has been made to withdraw Jason from the team.

"This will allow him time to refocus his efforts for his assault on the London 2012 Paralympic Games.

"We are still looking forward to success in Christchurch - the team is small but strong and all eyes will be on Michael McKillop, current world record holder in the 800m, and Orla Barry, European record holder in discus."

Without Smyth, Ireland's medal hopes at the competition rest on the eight remaining athletes who secured qualification in New Zealand.

They are a blend of youth and experience with names such as McKillop, Barry and Garrett Culliton alongside World Championship debutants Ray O'Dwyer, Ailish Dunne and Nadine Lattimore.

The Games will be held in Christchurch from January 21-30.

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