"It's about getting the skills back up to speed. Coming back to rugby you have to use a lot more mental aptitude. Mixing it up physically won't stress me too much. But there's a lot of hard work to go," he said.
A possible tilt at making the All Blacks Sevens for the Rio Olympics in 2016 is not open for discussion at this stage, though he and manager Khoder Nasser will surely have a plan around that.
Williams, regarded as a model professional with his approach to training, recorded the fifth best Chiefs' time in the yoyo test, an anaerobic endurance exam which has replaced the dreaded old beep test as a measure of a player's conditioning.
"Sonny was impressive... he's in good nick and it was a really good signal him coming in and being in that sort of condition on January 5," said Chiefs coach Dave Rennie, himself on the verge of inking a new deal with the Chiefs.
The signings of Williams and Taranaki's Seta Tamanivalu have given real depth and options to the Chiefs midfield, and will allow the team to play multiple styles outside of Cruden at pivot. Maori All Blacks captain Charlie Ngatai could well form a lethal 12-13 partnership with Williams, as he is stronger in defensive systems than the raw but explosive Tamanivalu.
"From an All Blacks point of view, we have to manage those top tier players. We've got a good group and good depth and a chance to play a big guy and a quick guy and some variation around that, or two big guys," said Rennie, unconcerned about a possible injury to Williams in his boxing bout, just a fortnight before the Chiefs launch their campaign against the Blues.
"The key thing is that he plays well for us. A lot of people want to go to a World Cup, but they've got to play well in Super Rugby first."
Williams has always said that boxing, and the requisite intense training, helps, rather than hinders, his rugby.
"It's just so physically challenging. The boxing refreshes me mentally and gets me away from anything else. It's so scary and daunting, so it gets me in a place where nothing on the field will faze me after the boxing. It's just so uplifting, not just as a rugby player but as a person.
"I haven't been blessed with the skills to be a rocket scientist. I'm fortunate to be blessed to be able to play rugby or try my hand at boxing. I'm a father now and it really puts it into perspective. Sport is just sport. I just want to be the best father and husband I can be."
*Rennie also confirmed that departing assistant coach Wayne Smith will look after the Chiefs' 2015 counter-attack, with the defence portfolio passing to Andrew Strawbridge.
