Trump campaign senior adviser Jason Miller said in a statement they had already agreed to the same terms as CNN's June debate, which had muted microphones, adding: "We said no changes to the agreed-upon rules."
But Trump later told reporters that he preferred to have his microphone kept on, adding that he did not like it muted last time and that he was not preparing much for the face-off against his new rival.
"Doesn't matter to me. I'd rather have it, probably, on. But the agreement was that it would be the same as it was last time," Trump said.
"I'm not spending a lot of time on it. I think my whole life I've been preparing for a debate," Trump added. "You can't cram knowledge into your head, for you know, 30 years of knowledge in one week. So, you know, there's a little debate prep, but I've always done it more or less the same way."
Representatives for ABC did not immediately respond to a request for comment.
Harris secured the Democratic nomination after President
Joe Biden stepped aside last month, and had said they would do the Sept. 10 debate hosted by ABC News previously agreed to by Biden and Trump.
Biden had
pushed for earlier debates, hoping to boost his campaign and cast a brighter light on Trump. But his own halting performance at the June 27 face-off triggered alarm within his party, with him ending his reelection bid weeks later.