The Six Nations has "blown the World Cup wide open," says former Italy and South Africa coach Nick Mallett.
Ireland clinched back-to-back titles on a thrilling final day and Mallett believes a northern hemisphere side can now go on to win the global showpiece.
"Northern hemisphere teams are capable of playing with pace and skill, they have huge physicality and deadly goal-kickers," he told BBC Radio 5 live.
"It was a great advertisement for northern hemisphere rugby."
Mallett was in charge of Italy at the last World Cup in 2011, which New Zealand won on home soil. But he feels Steve Hansen's side will find it hard to retain the Webb Ellis trophy come October.
He added: "I don't think you can say New Zealand are necessarily very confident of winning this World Cup, coming to the northern hemisphere and having to play teams like Ireland, England or Wales, who have made appreciable improvements in the past few years."
The final day of the Six Nations produced 27 tries, with England, Ireland and Wales all playing attacking rugby in a bid to claim the Championship on points difference.
And Mallett, who worked with rugby statistical analysts at Accenture during the tournament, says supporters in the southern hemisphere will have watched the last round of matches with interest.
"I can promise New Zealanders, South Africans, Australians and Argentinians were watching, and probably what was spoken about was 'why on earth can't northern hemisphere teams play like that all the time?'
"It's all in the mind-set of the coaches and the players."
Mallett was interviewed for the position of England head coach in 2012 and has urged the current incumbent Stuart Lancaster to keep faith with his midfield combination, even though the likes of Owen Farrell, Brad Barritt and Manu Tuilagi are all set to return from injury for the World Cup.
|England kick-off the 2015 Rugby World Cup against Fiji at Twickenham on September 18|
"England have expanded their ability to attack, with [George] Ford at fly-half and the introduction of [Jonathan] Joseph. So they are a much more exciting and more dangerous team," Mallett said.
"To get rid of that backline because of a perceived need to be more conservative at the World Cup is negative thinking.
"But the stronger the depth in your squad, the better chance of winning this tournament, and England have got a lot of strength in depth at the moment."