Warner, 36, has just one Test century in the past three-and-a-half years - a cathartic 200 against South Africa during the 2022 Boxing Day Test in Melbourne.
Three cheap dismissals and a fractured elbow during the subsequent tour of India invited speculation that his 103-cap career could be coming to a close, with the likes of Usman Khawaja, Marcus Harris and Travis Head all options at the top of the order.
But he was named in Australia's squad for next month's World Test Championship final against India, as well as the first two Tests against England, and appears to have McDonald's faith.
"We're optimistic with what Dave's got left," McDonald told SEN Radio.
"We've picked him in the squad and we feel that he's going to play a really significant part in the Ashes and the World Test Championship final.
"That's why he's on the plane. We think he's got some good games left in him. He's clearly in our plans.
"He knows exactly where he sits with us and internally we're really settled around what we need to do and how we're going to go about it."
England bowler Stuart Broad said this week he was excited to renew his rivalry with the left-hander, having dismissed him seven times in 10 innings during a 2019 Ashes series that saw Warner average just 9.5.
McDonald prefers to focus on better days and is confident Warner can acquit himself well.
"In 2015, I think it was eight half-centuries and he averaged mid-40s. So, he's had success there. It's not as though he hasn't had success in those conditions," said McDonald.
"We're backing him to draw on everything that he's got. Leading into the Boxing Day Test the doomsday people were out there as well."
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