All Blacks midfielder Sonny Bill Williams will make an announcement on his future at a press conference in Hamilton on Monday, the New Zealand Rugby Union has confirmed.

He will be joined by All Blacks assistant coach Ian Foster and Chiefs coaches Dave Rennie and Wayne Smith.

Speculation is mounting that Williams is heading overseas to play club rugby in Japan before making a return to rugby league next year.

He is expected to announce his decision to play for Japan Top League team Panasonic in a 10-match deal said to be worth $800,000, The Daily Telegraph says.

Other media report the figure to be as much as $1.7 million.

The Top League season begins on August 31, running until the end of January, after which Williams is expected to sign with NRL team Sydney Roosters.

Williams controversially walked out on Canterbury mid-season in 2008, joining French rugby club Toulon.

He was part of last year’s Rugby World Cup-winning All Blacks team, and showed commanding form in the three-Test series against Ireland last month.

Williams, who is nearing the end of a one-year deal with Super Rugby franchise the Chiefs, is also expected to continue his fledgling boxing career.