''Lachie was subbed out last week with a bit of blurred vision, but that was the only issue,'' McDonald told The Age’s Samantha Lane.
''He was trying to get his focus. He passed all the concussion tests, but he still had blurred vision so we just thought, 'Nup, we're not going to risk it' … we're very confident he wasn't concussed.''
McDonald says Daniel Wells (calf) and Nathan Grima (hamstring tendonitis) will also be in line for selection.
''All three boys are tracking in the right direction, it's just a matter of them getting through training on Thursday afternoon.'
''We wouldn't be taking any risks with anyone, so we wouldn't be playing Wellsy or Grima, especially on the back of soft-tissue injuries … and Lachie's the same.''
Sam Wright is also expected to prove his fitness after being replaced in last week’s side by Aaron Mullett.
Meanwhile McDonald has told the Herald Sun’s Matt Windley the conditions in Perth won’t faze the Roos, despite a forecast temperature of 27C on Sunday.
"It's going to be warm over there so I'm sure our conditioning guys will react accordingly," McDonald said.
"But our guys have played over there in those conditions before, so we'll be prepared for all of that."
The match will start at 1.15pm (3.15pm Melbourne time) when the mercury is reaching its peak. Day matches in Perth usually start at 2.40pm, but the broadcasting requirements of Channel 7 have altered the timing of the first bounce.
North will be unable to train at Patersons Stadium before the game because the ground is booked out for an International rugby match between Australia's Wallabies and South Africa.
The team will train at Leederville Oval on Saturday instead, the home of WAFL club Subiaco.
