Donald Trump. Pool/Getty Images

President Donald Trump acknowledged in an interview with The New York Times published Wednesday that there was a certain red line he thought special counsel Robert Mueller shouldn't cross while carrying out the Russia investigation: digging into his finances.

On Thursday, it emerged that Mueller was expanding his investigation to do just that.

Asked by Times reporters Michael Schmidt and Maggie Haberman about whether an investigation into Trump's finances would be a breach of a "red line," Trump answered, "I would say yeah."

"By the way, I would say, I don't — I don't — I mean, it's possible there's a condo or something, so, you know, I sell a lot of condo units, and somebody from Russia buys a condo, who knows?" Trump said. "I don't make money from Russia. In fact, I put out a letter saying that I don't make — from one of the most highly respected law firms, accounting firms. I don't have buildings in Russia. They said I own buildings in Russia. I don't.

"They said I made money from Russia. I don't," Trump continued. "It's not my thing. I don't, I don't do that. Over the years, I've looked at maybe doing a deal in Russia, but I never did one. Other than I held the Miss Universe pageant there eight, nine years."

Trump said digging into his finances would be a "violation" of what the investigation was supposed to focus on. Bloomberg reported Thursday that Mueller was expanding the Russia investigation to include Trump's business dealings.

"Look, this is about Russia," he said. "So I think if he wants to go, my finances are extremely good, my company is an unbelievably successful company. And actually, when I do my filings, people say, 'Man.' People have no idea how successful this is. It's a great company. But I don't even think about the company anymore. I think about this.

"'Cause one thing, when you do this, companies seem very trivial. OK?" he continued. "I really mean that. They seem very trivial. But I have no income from Russia. I don't do business with Russia. The gentleman that you mentioned, with his son, two nice people [Russian billionaire Aras Agalarov and his pop-star son, Emin]. But basically, they brought the Miss Universe pageant to Russia to open up, you know, one of their jobs. Perhaps the convention center where it was held. It was a nice evening, and I left. I left, you know, I left Moscow. It wasn't Moscow, it was outside of Moscow."

Trump did not confirm to The Times how he might respond if Mueller were to cross the red line.

"I can't answer that question because I don't think it's going to happen," he said.

Earlier in the interview, Trump mentioned that Mueller had interviewed for the vacant FBI director post after the president ousted James Comey from the position in May. Trump expressed shock that Deputy Attorney General Rod Rosenstein named Mueller as special counsel "the next day" following the job interview.

"I said, what the hell is this all about?" Trump said. "Talk about conflicts? But he was interviewing for the job. There were many other conflicts that I haven't said, but I will at some point."

Mueller is tasked with overseeing the investigation into Russian interference in the 2016 presidential election, and that includes whether Trump's campaign colluded with Russian officials. Mueller's team is already investigating the finances of White House senior adviser Jared Kushner, with federal prosecutors also taking a look at the financial dealings of Trump associates such as former campaign chairman Paul Manafort and former National Security Adviser Michael Flynn.