Elon Musk is willing to invest between $10 billion and $15 billion of his own money to take Twitter Inc (TWTR.N) private, the New York Post reported on Tuesday, citing two sources familiar with the matter.

The billionaire, who is Twitter's second-biggest shareholder with a 9.1% stake, is planning to launch a tender offer in about 10 days and has tapped Morgan Stanley to raise another $10 billion in debt, according to the report.

Musk, who is also Tesla Inc's (TSLA.O) chief executive, may also be willing to borrow against his current stake if necessary, a move that could possibly raise several billion additional dollars, the New York Post reported.

Twitter declined to comment. Tesla did not immediately respond to a Reuters request for comment from Musk.

The social media company adopted a "poison pill" last week to protect itself from Musk's $43 billion buyout offer.

More private-equity firms have expressed interest in participating in a deal for Twitter, people familiar with the matter told Reuters on Monday without naming the firm.

The interest emerged after Thoma Bravo, a technology-focused PE firm, contacted the social media platform last week to explore a buyout that would challenge Musk's offer.

Apollo Global Management Inc (APO.N) is considering ways it can provide financing to any deal and is open to working with Musk or any other bidder, the sources told Reuters.

Many investors, analysts and investment bankers expect Twitter's board to reject Musk's offer in the coming days, sayingit is inadequate.

Twitter shares were down 1.6% at $47.69 in afternoon trade, well below Musk's offer of $54.20.