Short seller Jim Chanos hit back at Elon Musk on Wednesday, accusing the billionaire entrepreneur of over-promising on Tesla and The Boring Co.'s capabilities.

"What bothers me is not so much the personal stuff and the personal attacks. I'm used to that. It's the willingness to say things that I think he knows are a stretch, to be polite," said Chanos, who has been betting against Tesla for years.

"I don't think you get to tell people you're going to make 20,000 Model 3s a week when you know that's not going to be the case," Chanos added, referring to the problems hampering production of Tesla's Model 3, a less expensive electric sedan aimed at the mass car-buying market.

Chanos, founder of Kynikos Associates, also said in a "Fast Money Halftime Report" interview that he believes Musk has been making similar "stretch" promises about the private, transit tunnel-digging venture The Boring Co.

"You don't get to tell the city of Chicago, I'm going to be build a tunnel and do it in a couple of years for a billion dollars through 20 miles of residential area. You know that's probably not going to happen," he said.

Chanos also denied Musk's allegations in a tweet about getting insider information and paying journalists.

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In addition to Business Insider, Musk earlier this month lashed out at Reuters and CNBC.

"We talk to journalists all the time. We have never received insider information from any journalist at any time, including Tesla. And we've never paid any journalists," Chanos said.

"These are serious charges," he added. "When you make serious charges, you ought to bring serious evidence."

Chanos pointed to what he said was the same type of pattern when Musk came under fire this week for a string of controversial tweets, including an attack on one of the British divers involved in the rescue of the Thai soccer team.

The billionaire's recent social media blitz comes after he cut off an outspoken Tesla bear during a post-earnings analyst call in May.

Chanos, who spoke from the eighth annual CNBC and Institutional Investor Delivering Alpha conference, has frequently blasted Musk's leadership at Tesla. In April, the short seller said Musk, "may be misleading investors."

Short selling is a practice in which traders can bet against a company by selling shares they don't own and buying them back at a lower price.

Chanos has always been rather vocal on many of his big trades. He was one of the early fund managers to waive the red flag on the one-time high-flying energy giant Enron, which was eventually revealed as a fraud.

In August 2000, Enron hit an all-time high of $90.56 per share. It filed for bankruptcy 16 months later.

Tesla did not immediately respond to CNBC's request for comment.

— CNBC's Matthew J. Belvedere contributed to this report.

Correction: Elon Musk cut off an outspoken Tesla bear during a post-earnings analyst call in May. An earlier version misstated the month.