North Melbourne have been weakened by the loss of reliable defender Scott McMahon on the eve of Sunday's clash with Port Adelaide at Etihad Stadium.

Roos assistant coach Darren Crocker said the side was forced to leave the No.1 defensive player from last season out of the side.

"He tweaked a groin at last week and hasn't come up and he'll miss," Crocker said.

North remain heavy favourites to beat the Power who have slumped to 12th on the AFL ladder after a string of five losses, but they say they will not be complacent against the side which they fell to in round one.

"We know what an environment is like when you've lost five on the trot and they will be desperate for a win so we expect a pretty built-up Port to come out and give a fairly fearsome attack on this game," Crocker said.

But he said, with the Roos now poised to move into the eight - a win would give them a 7-6 scoreline - the players' confidence was higher as they adapted more to senior coach Brad Scott's game plan.

"I think our blokes' self belief is really growing - the last two wins have been tremendous for our group, especially last week against Carlton, who are obviously travelling along nicely," he said.

"It would be great to get our seventh win on the board going into the break and then look forward to the back half of the year."

Crocker said the players were now responding better each week to Scott's strategy.

"The signs are definitely there with the guys who have been playing at senior level for a period of time," he said.

"They are starting to grasp what we're after with our concepts and structures that we've put in place.

"The test is going to come when at times we bring a new mix into the team, and how quickly they can actually adjust to it as well," he said.

"But we're really pleased with where the group's at in relation to taking on board the way we want to play and understanding what's required."

Port, without key forward Warren Tredrea, have struggled to kick goals but they will have an edge tactically with former North senior coach Dean Laidley now in the Power box as an assistant coach.

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