All Black Sonny Bill Williams concedes he'll have to make adjustments fighting an opponent the same size as himself for the first time.
The 26-year-old has confirmed his next boxing bout against Richard Tutaki for the New Zealand heavyweight title in Hamilton next February.
Tutaki is a 10-year professional boasting a 19 win-21 loss record, with one draw.
But Williams is backing his fitness and speed to get him through the bout.
The fight will take place just two and a half weeks before his new Chiefs franchise open their Super Rugby season.