World Cup News:The pressure of qualifying for the knockout phase of the World Cup is preventing Northern Hemisphere sides from playing their best rugby according to New Zealand assistant coach Steve Hansen.

While New Zealand, Australia and South Africa have booked their places in the quarter-finals with ease, the Six Nations sides are all still battling to try to secure a berth in the last eight.

France will make the quarters if they beat Georgia but Ireland are face an early exit unless they can get a bonus point against Argentina and prevent the Pumas getting one themselves.

England and Wales are confronted with tricky all-or-nothing encounters against Pacific islanders Tonga and Fiji, while Scotland and Italy go head-to-head in search of a place alongside the All Blacks in their pool.

"Some of them will be very disappointed," said Hansen. "Ireland will be scratching their heads wondering what's gone wrong. But I think France are growing in confidence with every game which makes them dangerous . . . they certainly dealt with Ireland pretty effectively. England have got a big challenge on their hands against Tonga."

Hansen, who coached Wales at the last World Cup, said he expected the form of the established European nations to change in the knockout stage. "Things can change. I know from my experience with Wales we struggled because of the pressures of the round robin to qualify and once we knew we'd qualified we lost our inhibitions and played some really good rugby. That's what's been happening a wee bit with the European sides. They are finding the pressure of qualifying tough and it might be inhibiting their play"

Meanwhile, the balls used at the tournament are to be investigated following complaints from New Zealand outhalf Dan Carter. Carter, who missed five out of nine place-kick attempts against Scotland, is unhappy the balls players have been given in practice are different from those used in the matches.

And Greg Thomas, the International Rugby Board's head of communications, admitted the organisers have asked manufacturers Gilbert to examine Carter's comments. "There should not be any difference between the balls given to teams for training and those used in matches," Thomas said. "We have asked Gilbert to look into the matter. They are carrying out an inquiry."