SpaceX has been fast-tracked into the Nasdaq-100 Index, meaning the stock performance of Elon Musk’s rocket company is now directly tied to the retirement accounts, mutual funds and portfolios of millions of everyday American investors.

But self-proclaimed market "permabear" and GMO co-founder Jeremy Grantham is heavily skeptical of the company's valuation and long-term investment thesis.

"Everyone’s lining up to tell you to buy the craziest IPO in the history of man," Grantham told Morningstar’s "The Long View" podcast. "In 50 years, they’ll be telling and writing stories about SpaceX, and they’ll be quoting you paragraphs from the prospectus, and you will be laughing at it."

D.O.G.E. WEBSITE DEACTIVATES AFTER REACHING SELF-TERMINATION DEADLINE: ‘COME TO AN END’

"In the end, the reality will come out, and this will turn out to be, of course, one of the landmark historical events that I so value in history looking back," Grantham continued. "It will be amazing, by the way, if it doesn’t collapse, because it will need such massive developments on AI that our entire lives are totally different."

SpaceX made its IPO debut on June 12, and began trading at $150 a share, above its listing price of $135 a share. As of midday Wednesday, the stock hovered around $149 per share and was down nearly 7% month-to-date.

Goldman Sachs, JPMorgan and Morgan Stanley have posted bullish forecasts for SpaceX's valuation, Fortune reported, with price targets ranging from $205 to $300 per share.

Grantham also criticized Wall Street's advice for clients to buy SpaceX, adding that even if the market ultimately validates the elevated share price, society will become a "strange one" where "we’ll be lucky not to be bossed around by our automaton friends."

SpaceX's quick addition to the Nasdaq-100 Index has affected its stock performance, with Grantham also saying, "What that means is there’ll be a lot of people who have to buy it for any index that is Nasdaq-y. So there’ll be much more demand than there are sellers."

"So supply and demand being what it is, it’s hard to imagine the price won’t go up, and perhaps it will go up a lot," Grantham said.

SpaceX's IPO raised $75 billion and was the largest IPO in history, surpassing Saudi Aramco's $29 billion IPO in 2019.

GET FOX BUSINESS ON THE GO BY CLICKING HERE

The IPO cemented Musk's status as the world's richest person, pushing the value of his holdings toward $1 trillion, a milestone no individual has previously reached.

Founded by Musk in 2002, SpaceX has grown into the world's largest space company and a dominant force in commercial launch services. The company pioneered reusable rocket technology, helping lower launch costs and reshape the economics of the space industry. It has also become a key contractor for NASA and the U.S. government through civil and national security missions.

READ MORE FROM FOX BUSINESS

FOX Business’ Eric Revell and Bradford Betz contributed to this report.