Canterbury will be without Sonny Bill Williams for another week after coach Rob Penney confirmed the former NRL star isn't ready for the national provincial championship rugby match against Auckland this weekend.

Williams has yet to represent his new province and it won't be until at least the sixth-round fixture against Bay of Plenty on September 3 that he makes his debut.

He has been recovering in recent weeks from a tight hamstring suffered during 50 minutes for his Christchurch club Belfast, his only rugby match since returning to New Zealand from French club Toulon to pursue an All Blacks jersey.

Penney said Williams' lack of rugby meant it would be an enormous risk to select the 25-year-old, a risk he wasn't prepared to take.

"It would be really unfair to make that call, for all sorts of reasons," Penney told Radio Sport.

"He just hasn't had any game time under his belt so to expect him to come up and perform against a team like Auckland at this stage, I think would be a bit unusual and a bit unfair."

Penney said if Williams is fit he may well play in the curtain raiser at Christchurch on Saturday, a match involving club players.

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