The Tesla boss has been on a selling spree over the past year, during which he has cashed out roughly $32 billion worth of shares in the electric-vehicle maker. That includes around $8.5 billion of sales in April, while Mr. Musk was lining up financing to take over Twitter. At the time, he tweeted: “No further TSLA sales planned after today.”

Neither Tesla nor Mr. Musk responded to a request for comment.

Mr. Musk has since tried to walk away from buying Twitter, which is suing him to enforce the takeover. The case is headed to court in October.

If the judge were to force Mr. Musk to consummate the transaction, he could be on the hook for more than $33 billion in equity financing, according to a regulatory filing. He already owns more than 9% of Twitter, valued at roughly $4 billion at $54.20 a share, Mr. Musk’s buyout price.

Asked on Twitter if he was done selling shares, Mr. Musk tweeted, “Yes.” (He also said in April that he wasn’t planning additional sales.)

On Tuesday, he added: “In the (hopefully unlikely) event that Twitter forces this deal to close and some equity partners don’t come through, it is important to avoid an emergency sale of Tesla stock.”

If the Twitter deal doesn’t close, Mr. Musk would buy Tesla stock again, he said. He also suggested he might set up his own social-media platform—X.com—if the deal falls through. He said before agreeing to buy Twitter that he was “giving serious thought” to such an endeavor.

Mr. Musk, whose net worth totals around $250 billion, according to the Bloomberg Billionaires Index, is compensated in stock awards and doesn’t accept a salary from Tesla.

He had long been reluctant to sell shares in the company, which could weaken his control. Much of last year’s sales were designated to cover tax withholding obligations associated with exercising stock options.

Last week, Tesla shareholders cleared the way for a 3-for-1 stock split that the company has said is designed to make ownership more accessible to employees and individual investors.

The split is due to take effect Aug. 25 for shareholders of record on Aug. 17, the company said last week.

Write to Rebecca Elliott at rebecca.elliott@wsj.com