Elon Musk, the billionaire CEO of Tesla and SpaceX, is reportedly facing a criminal probe by the Justice Department into Musk's Aug. 7 tweet about taking Tesla private. The investigation is just the latest piece of bad news for Tesla and Musk, who has faced growing criticism over his recent behavior.

But, at least Musk has Neil deGrasse Tyson on his side. The famed astrophysicist recently had some strong words for Musk's critics.

"Can they leave him alone?" Tyson asked in a recent interview with TMZ, posted on YouTube Sept. 12. Tyson was referring to the criticism that has been heaped upon Musk, the CEO of Tesla and SpaceX, after he was filmed drinking alcohol and smoking marijuana during a podcast interview with comedian Joe Rogan in early September.

"Let the man get high if he wants to get high," Tyson said to TMZ about Musk.

With regard to the regulatory investigation of Musk's tweet, however, the scientist Tyson noted that, as the CEO of a public company, Musk must be held accountable to federal financial laws. "He's got to obey the SEC, clearly … there's an accountability to the public trust," Tyson told TMZ.

Marijuana is legal in California, where Musk was filming the podcast, but critics said the incident was the latest example of erratic behavior from the billionaire. Tesla board members have reportedly expressed concerns in the past about Musk's use of recreational and prescription drugs, according to The New York Times. Now, as CNBC previously reported, Musk may have violated Tesla's business conduct policy by imbibing alcohol and marijuana while representing the company during the podcast.

Meanwhile, Musk has also made negative headlines recently by insulting a British cave diver who helped rescue boys trapped in a Thailand cave, and the CEO is also facing an SEC investigation into his August tweet suggesting he might take Tesla private.