After 49 innings without a Test century, Labuschagne looked a tortured soul by the end of Australia's 2-1 series defeat in South Africa, dismissed twice in eight balls in the Cape Town decider with his only runs coming via a leading edge.
The 32-year-old is likely to be dropped for the first home Test against New Zealand in December, while McDonald confirmed selectors would have to "reassess" Labuschagne's status.
Criticism has come in thick and fast for Australia following Saturday's 176-run defeat, and in particular their continual selection of Labuschagne.
The world's former top-ranked batter was briefly dropped for three Tests in the Caribbean last year, but was recalled for the home Ashes after two tons in four Shield games.
Former Test opener Simon Katich even went as far as to suggest on Saturday the selection panel of George Bailey, McDonald and Tony Dodemaide had "crucified" the Queenslander by not dropping him earlier.
"It's been very obvious to everyone watching this series they've got this horribly wrong," Katich said in SEN's commentary.
"What they've got more horribly wrong is they've potentially crucified a bloke's career … He might not come back from this."
McDonald would not respond directly to those comments when put to him, but was adamant it was never a negative for a player to be picked for Australia.
"Any opportunity that you get to play for Australia, I don't think damages you," McDonald said.
"There's been a lot of even critiquing of some of our younger players where they've been placed and the harm that that may cause to their careers.
"You don't get the perfect place all the time for everyone. Sometimes people have got to play against India. Sometimes people have got to go to subcontinent."
Labuschagne's run without a century is the longest of any top-four batter for Australia in history.
There had been a feeling the Queenslander could go after the drawn series against Bangladesh, before he was backed for South Africa.
Asked directly if Labuschagne would be selected for the start of the home summer, McDonald said he would not rush decisions amid the emotion of a series loss.
"He's had some opportunities that he's missed on this tour in particular. So that'll be something in the next week or so that we'll get our heads around," he said.
"We believed in Marn for this tour. We'll have to reassess that as we move forward.
"There's still a very good cricketer there every time he drops back to state level, he outperforms the others.
"But there's some state careers going on at the moment as well which is going to give us a great runway for what the New Zealand selections will look like also."
Sam Konstas is one player performing in the Shield, and would fit the bill of a youngster who selectors believe is now benefitting from an early stint in Test cricket.
Meanwhile, McDonald insisted there was no need for added scrutiny of Nathan Lyon, after he was unable to get the same kind of results as South Africa spinner Simon Harmer in Cape Town.
Lyon took 2-101 for Australia as South Africa went from 4-140 and leading by 40 at the start of day four, to being able to set the tourists 288 for series victory.
Harmer then got on a roll for the Proteas on the fifth day, taking 6-16 as Australia struggled to deal with his turn out of the rough.
Australia's captain Pat Cummins defended Lyon afterwards, insisting he had bowled well without taking wickets, while McDonald indicated he remained the No.1 spinner for the start of the home summer.
"We sit back and we'll go through Shield cricket. Nathan will be preparing for the first Test match in Perth," he said.
21°C