The 33-year-old has endured an injury-plagued Super Rugby season as rivals for a midfield spot have flourished, raising doubts about whether he remains an automatic selection for the defending champions.

The two-time World Cup winner played for 60 minutes in last weekend's draw against South Africa and coach Steve Hansen has shown faith by including him in the 34-man squad for the two Tests against Australia.

But Hansen also told Williams to miss the first clash with the Wallabies in Perth on August 10 and instead work on his fitness playing provincial rugby with Counties Manukau.

The 52-Test veteran, who had knee surgery in April, downplayed the significance of the issues he is facing.

"For those that say I'm under pressure playing a game that I enjoy. Get your priorities right," he tweeted.

"Look at what's going on in the world. Starving children, the single mother raising three kids, the atrocities refugees are facing around the world, racism. This is what I call pressure."

Williams is one of five centres vying for four spots in New Zealand's World Cup squad, along with Ngani Laumape, Anton Lienert-Brown, Jack Goodhue and Ryan Crotty, who is recovering from a broken thumb.

Hansen said pitching Williams into provincial rugby gave him the opportunity to get more game time before selectors named their 31-man World Cup squad later this month.

"Then everybody gets judged fairly and whatever combination of the four we come up with, everybody has had an opportunity to say 'Well, I've had a fair go'," he said.

"Every one of them deserves that, including Sonny."

Williams, who won World Cups in 2011 and 2015 after switching from rugby league, hinted back in February that injuries could mean this season is his last.