"Yes, it is still true. I hope I can make it happen. I made the people of Australia a promise, I will keep that promise if it happens.
"I'm not a money driven person. My parents always taught me with money you should achieve things that help others and help the people that actually need the money.
"Four million dollars would be nice. I mean, it would be very, very nice. I could maybe buy myself a few cars or something.
"But there is people that actually need it for their homes, for rebuilding wildlife, rebuilding houses, rebuilding the life that they once knew. So it's much more important that they get that."
Fires have ravaged large parts of Australia, leaving 33 people dead and thousands of homes destroyed, with sports stars around the world rallying to support recovery efforts.
The young German spoke about the donation further in his press conference when he was asked about the pledge by a journalist.
"It's a lot of money for me. I'm not Roger (Federer), I'm not LeBron James or something like that, this is still big," he said.
"But at the same time I know that there are people right now in this country, in this beautiful country that lost their homes and actually they need the money.
"They actually depend on it. Building up their homes again, building up their houses and building the nature that Australia has and the animals as well.
"There's much better use for those people with that money than I have right now."
If Zverev beats Thiem tonight, he will play Novak Djokovic in the final.
