Elon Musk’s deal for Twitter has features that make it risky, including billions of dollars of personal debt. If it goes wrong, it could burn Tesla shareholders and strain Twitter’s financial health.

There are already signs of investor concern. As Tesla has become one of the world’s most valuable companies, its stock has become widely owned by retail investors through mutual funds and other investment vehicles. But it has fallen 24% since the disclosure early last month that Musk had taken a sizable stake in Twitter, a period in which the S&P 500 has declined 10%.

"Even if he’s able to finance it, it just is not a sensible deal from a financial perspective,” said Aswath Damodaran, professor of finance at New York University’s Stern School of Business.