Scrutiny of Barrett grew after the 112-cap All Blacks squandered a certain try when he stepped on the deadball line in his side's 20-13 loss to the Waikato Chiefs last weekend.

That error, coupled with a disappointing kicking display, has added to concerns over Barrett's form but McGrath retains full belief in the 31-year-old's ability.

"First and foremost Beauden is a world-class player," McGrath said, according to the New Zealand Herald. "By his own standards he'll know that wasn't his best performance but it's a collective team too. He'll be fine. He's hungry.

"He's an ultimate pro. He's heard outside noise before. I'm sure he doesn't read the papers or have a Facebook page. He's about getting his job done and we're thoroughly behind him but it's not just on one person."

The Blues are fifth in the standings on 16 points, 11 behind the table-topping Chiefs, having won three and lost three of their six matches.

"It's Beauden Barrett. He's been there done that," Blues captain Dalton Papalii said. "He's that much of a veteran and professional he knows where he's at.

"We haven't been in form as a whole team so there's no point pointing the finger, we have to work together to get solutions and wins.

"This is the week we're going to try put it all together and make the masterpiece."