Musk reportedly made the comments while speaking at a summit hosted by Chamath Palihapitiya, Jason Calacanis, David Sacks and David Friedberg for their “All-In” podcast.
The stock closed down more than 8% as investors fear Musk will walk back on his agreement to acquire the social media company for $44 billion.
Twitter shares have also erased all gains made since Musk disclosed his investment in the company on April 4, in part thanks to a sell-off late last week. Musk said Friday that the acquisition was “on hold” while he researches the proportion of fake and spam accounts on the platform, which he believes Twitter has misstated.
Musk on Monday estimated that fake users make up at least 20% of all users, according to the Bloomberg report. Twitter, meanwhile, has said the accounts made up fewer than 5% of its monetizable daily active users in the past quarter.