Halfback Kyle Preston is poised for a test debut off the bench for the All Blacks against South Africa on Saturday at Eden Park in the Rugby Championship.

The Crusader's backing up Finlay Christie, who's been named to start with Cortez Ratima ruled out due to an injury.

All Blacks assistant coach Scotty Hansen says experts confirmed Ratima wasn't fit to play this time round.

"It wasn't an option this week to play him." 

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