NSW Waratahs coach Ewen McKenzie fears the effect the bye will have on the Crusaders ahead of their Super 12 crunch match at Aussie Stadium on Saturday night.

The undefeated Waratahs' clash with the four-time Super 12 champions will be their toughest test to date, especially with the Crusaders coming off a week's break.

The Kiwi powerhouses are noted for the way they seem to reinvigorate themselves during their week off.

Last season they dropped two of their opening three games before the bye. After the break they won six of nine games before eventually going down to the ACT Brumbies in the final.

But this year their form before the bye was superb, with their only blip being the opening round loss to the Brumbies.

Despite playing one less game than most teams, the Crusaders have scored the more points (171) than any other side.

"They've normally been slow starters in the competition and they've used the week off to be the catalyst for them to really kick off," McKenzie said after Waratahs training on Monday.

"That's how they've done it year in year out so this is a bit of a different year for them. I'm kind of hoping that their really good form's out there and the week off is going to work in reverse, but I don't think I'll be that lucky."

McKenzie said while the Crusaders' much-vaunted attack would provide a stern test for the Waratahs, it was their defence that was causing most concern.

"If you look at the stats, they're feeding off turnovers more so than any other side," McKenzie said.

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