SpaceX approved the $1 billion loan, which was backed by some of Musk's SpaceX stock, in October and Musk drew all of it down the same month, according to the Tuesday report, citing documents. Musk took ownership of Twitter in October.

Musk has had arrangements with banks to borrow against his shares in his companies, including electric vehicles (EV) maker Tesla, while privately held SpaceX has served as his lender, the report said, adding that paying for Twitter further complicated Musk's financial situation.

Musk is SpaceX's largest shareholder with a 42% stake and almost 79% of its voting power as of March, the report said, citing a filing with the Federal Communications Commission. SpaceX had $4.7 billion in cash and securities on hand at the end of last year, the paper said, citing documents.

Both SpaceX and X did not immediately respond to a Reuters request for comment.

Elon Musk sold a massive chunk of his Tesla shares in 2022, both before and after the Twitter deal, bringing his total sales to about $40 billion which frustrated investors in the EV maker.

In April 2023, Tesla disclosed that it had further tightened rules around Musk using his stake in the company to borrow money, according to the WSJ report.

In addition to Tesla and X, Musk is a co-founder of brain-chip startup Neuralink.