The billionaire, Rolling Stone wrote, added: "I mean, she's a woman, and I'm not s'posedta say bad things, but really, folks, come on. Are we serious?"
On Fox News Thursday morning, Trump denied he was talking about Fiorina's looks, even as he conceded that the comments were reported accurately.
"Probably I did say something like that about Carly," Trump said. "I'm talking about persona. I'm not talking about look."
The flamboyant presidential candidate's remarks have already been used by his critics to reinforce the notion that he is misogynistic, a charge he has faced from conservatives and liberals alike.
The billionaire landed in hot water last month amid on ongoing feud with Fox News anchor Megyn Kelly, whose questions about Trump’s past statements directed toward women unnerved the candidate during the first GOP presidential debate. He later accused her of being unfair and at one point appeared to insinuate that the tough question was motivated by her menstrual cycle.
"She gets out and she starts asking me all sorts of ridiculous questions," Trump said on CNN. "You could see there was blood coming out of her eyes, blood coming out of her wherever. In my opinion, she was off base."
Fiorina, speaking to Kelly on Wednesday night about his most recent remarks, indicated that perhaps the ire is due to her recent bump in the polls. "Maybe, just maybe, I'm getting under his skin a little bit because I am climbing in the polls," she said.
Trump was also confronted by comedian Joy Behar during a prescheduled appearance Thursday morning on ABC's "The View."
"She failed miserably at Hewlett Packard. She failed at Lucent. … She then ran for the Senate; she lost in a landslide. Now she's running for president. I'm talking about her persona,” Trump said.
"Well then, why don't you talk about her brain instead of her face?" rebutted Behar.
“I’ve made a tremendous fortune. We need people that can change our country,” responded Trump, talking over Behar.
Former Florida governor Jeb Bush and Wisconsin Gov. Scott Walker both denounced Trump's remarks about Fiorina on Thursday morning on social media, with both calling the comments "inappropriate" for a presidential candidate.
Trump's escalating feud with Fiorina wasn't the only quarrel on his plate Thursday. He also struck back at his closest presidential rival, retired neurosurgeon Ben Carson, following Carson's Wednesday comments that seemed to question Trump's faith in unusually sharp terms.
Trump knocked Carson's characteristically calm demeanor -- and played down his medical accomplishments, saying he was only an “okay doctor.” (Carson was the first neurosurgeon to separate conjoined twins attached at the head.)
"He makes [Jeb] Bush look like the Energizer bunny,” Trump said on CNN Thursday morning. “Who is he to question my faith? ... When he questions my faith, and I'm a believer big-league in God, the Bible … I will hit back for that."
"He was a doctor … perhaps an okay doctor," he also said, adding that "Ben Carson will not be the next president of the United States."
Trump’s comments, the most aggressive he has made about Carson, came less than a day after the retired surgeon pointed to his faith when asked what he believes to be the biggest difference between himself and Trump.
"The biggest thing is that I realize where my success has come from, and I don't any way deny my faith in God," Carson said Wednesday night. "And I think that probably is a big difference between us."
During a speech in Washington at the same time as Trump's interview on "The View," Louisiana Gov. Bobby Jindal called Trump an "unstable narcissist" and said the businessman would ruin conservative chances of securing the White House if he became the GOP nominee.
“Like all narcissists, Donald Trump is insecure and weak, and afraid of being exposed. And that’s why he is constantly telling us how big and how rich and how great he is, and how insignificant everyone else is,” Jindal said. “We’ve all met people like Trump, and we know that only a very weak and small person needs to constantly tell us how strong and powerful he is. Donald Trump believes that he is the answer to every question.”
Meanwhile, a CNN/ORC poll released Thursday morning showed Trump surging to even greater heights in the polls, with the support of 32 percent of GOP voters. Carson had 19 percent, followed by Bush in third place with 9 percent.