Australia would be prepared to play Mitch Marsh as a specialist batter and pick only four bowlers for The Oval, if the in-form allrounder pulls up lame from Old Trafford.
Marsh lingers as one of Australia's two big fitness concerns for Thursday's fifth Test, with the other being Mitchell Starc's left shoulder after he was injured in Manchester.
Medical staff are confident that Starc will be fine to play at The Oval, after overcoming damage to his AC joint and continuing bowling the following day last week.
Marsh's fitness could have more significant ramifications, however, as Australia eye off their first outright Ashes series victory in England in 22 years with a win or draw.
One Test after playing both Marsh and fellow allrounder Cameron Green in Manchester, it's likely selectors will have to pick between the pair if they bring in Todd Murphy at The Oval.
Australia are yet to see the pitch for the final Test of the series, but the south London ground is renowned as one of the more spin-friendly venues in England.
If a selection squeeze is in place between Marsh and Green, the former has made a near-irresistible case to be the front-runner.
After he scored 118 while filling in for Green at Headingley, Australia may not have retained the Ashes with a draw at Old Trafford if not for Marsh's unbeaten 31 on day four.
In contrast, Green has not had the series he would have liked, averaging 20.6 with the bat and taking four wickets at 47 with the ball.
The only issue for Australia could be Marsh's ability to bowl.
Medical staff will keep a close eye on him in the lead up to Thursday, after he spent time off the field on day three with stiffness in Manchester and did not bowl after that.
If the issues continued, it could potentially leave Australia without a fourth seamer if Marsh was picked ahead of Green.
But despite that, McDonald said it would not necessarily prove an obstacle for Marsh.
"He's a little bit sore, hence why he was off the field. So I'm not going to hide that," McDonald said.
"Does it impact his position in the team? I think the team has played three quicks and one spinner, if we go that way, numerous times in the past.
"We have had the luxury of allrounders, or in particular Cameron Green, that's changed the shape of the team over time.
"But I mean, runs are premium first and foremost."
Australia's young prodigy as an allrounder a few months ago, Green now faces the possibility of time spent as Marsh's understudy.
The 24-year-old's dip in form comes during a six-month period where he has spent two nights in his own bed, with a Test series in India and the IPL.
"People probably draw some conclusions that that's affected the way he's gone about things here," McDonald said.
"But it's a little bit like Steve Smith, I think he's in a good space. He's working hard on his game.
"A lot of our batters are working on the right things and the way they go about it and runs are just around the corner."
