New Zealand fly-half Dan Carter ruled out for a month

Dan Carter (GETTY IMAGES)

Dan Carter, the New Zealand fly-half, may miss up to a month of the southern hemisphere Rugby Championship, which begins for the reigning champions against Australia on Saturday, after aggravating an old calf injury.

The absence of the two-time IRB World Player of the Year opens the door for Aaron Cruden or Beauden Barrett to slot into the playmaker position, but would also force coach Steve Hansen to re-consider his midfield options.

"It will give us plenty of food for thought over the next 24 hours," Hansen told said. "It does make us think who will cover inside centre."