All Black coach defends Sonny Bill rule change
All Blacks centre Sonny Bill Williams, pictured during a training session in Tokyo, on September 1, 2012 - by Toshifumi Kitamura
Williams, who is returning to rugby union after a second stint in Australia's National Rugby League, has been exempted from a rule that forces players to participate in the domestic ITM Cup before being eligible for All Blacks honours.
The move, announced this week, will allow Williams to slot straight back into the world champions' end-of-year tour to the United States and Europe.
"The reason why we want to take him on the end-of-year tour is because there's very limited Test matches between now and the World Cup," Hansen told RadioSport.
"If he was to be in a successful (Waikato) Chiefs (Super 15) side next year and they were playing in the final, for example, then he wouldn't be available for some of those Tests.
"It becomes difficult then to get him back into the ways of the All Blacks."
Hansen said Williams, who was part of New Zealand's 2011 Rugby World Cup triumph, was a proven performer in rugby union.
"You've got a quality, world-class player at your disposal and our job is to pick the best team. He's going to be one of the best players, so our job is to pick him," he said.
He said Williams, 29, who won the last of his 19 All Black caps in August 2012, had developed a keen knowledge of rugby union during his first stint in the code.
"He can watch a game of rugby now and understand it, which is massively important when you want to come back across," he said.
Williams' return will leave the All Blacks ample cover in the centres, with Conrad Smith, Ma'a Nonu, Malakai Fekitoa and Ryan Crotty available.
Hansen rejected suggestions that rushing Williams back would deny opportunities to emerging talent such as Fekitoa and Crotty, saying injuries had a way of ensuring that everyone had a run.
Williams began his career in rugby league, winning the 2004 NRL title with the Canterbury Bulldogs in his debut season before walking out on the team mid-contract to play rugby union in France.
He contributed to the New Zealand 2011 World Cup win and snared the 2012 Super 15 title with the Waikato Chiefs before returning to the NRL with the Sydney Roosters last year, picking up another title with the side.