Smith, one of the world's best batsmen over the last decade, replaced David Warner at the top of the order on the veteran's retirement from tests in January, allowing all-rounder Cameron Green to slot in at number four.

He has averaged 28.5 with a high score of 91 not out in four Tests but, in the absence of any other glaring weaknesses in the team, has come under scrutiny for his 51 runs over four innings in two tests against New Zealand.

"I think it's unfair," McDonald told reporters after Australia swept New Zealand 2-0.

"I don't think it's deserved. I think he'll be able to work through that. It's a new challenge for him, a new position.

"If you bring in a new opener and you gave them four Test matches, and then said, 'okay, we're going to shift that after four Test matches', would you think that's fair or unfair? I think it's reasonably unfair."

McDonald echoed skipper Pat Cummins's view that Smith remains one of the six best batsmen in Australia and said the batting group would be "hard to infiltrate."

"He is a great player and his ability to problem solve is one of his great strengths," he added.

"There will be a debate as to what his best position is... but he's up for the challenge, and I think any time that Steve Smith fails, he sees it as a greater challenge.

"So walking away here with 51 runs under his belt in tough conditions, that will no doubt drive him for the next challenge and that next challenge is India. They await, and I think it will be an internal motivator for him.

"He wants to open, it's a position that he came to us around, and we think he can make it work."

India are scheduled to play five Tests in Australia in December and January.