The 28-year-old former All Black centre, who helped the Sydney Roosters win Australia's National Rugby League championship on Sunday, has been linked with a return to Super Rugby's Chiefs where he was a member of Dave Rennie's title-winning team in 2012.
"Sonny is unavailable due to other commitments, and what they are at this stage I'm sure we would all like to know and I'm sure we will hear all about that over the next two or three weeks," Kiwis coach Stephen Kearney said.
"I spoke to Sonny and his agent yesterday. I have been working with them for quite some time in terms of his availability. I don't know (what he's doing)."
Williams, who returned for a second stint with the NRL on the strength of a handshake agreement with Roosters boss Nick Politis, has been tight-lipped about his future but has said he expected to make a decision on his career within weeks.
Rejoining the Chiefs would offer Williams the chance to revive his international rugby union career and the opportunity of a second World Cup appearance in 2015, having already been a member of the All Blacks team that clinched the Webb Ellis Cup on home soil in 2011.
Williams, who has mixed professional boxing with his rugby career, has also been offered a shot at a $1 million purse by a New Zealand promoter to take on the winner of a local heavyweight bout between Joseph Parker and 'King' Afa Tatupu.