The slump extended losses on Thursday after Hindenburg Research accused the electric-vehicle company and its CEO, Trevor Milton, of overhyping its truck's capabilities.

Citron Research backed up the claims on Friday morning and congratulated Hindenburg in a tweet, saying it was "exposing what appears to be a total fraud" with Nikola.

Milton fired back at the allegations in a tweet on Friday, accusing Hindenburg of wanting "max damage" with "false and deceptive" statements.

Nikola said in a press release that Hindenburg's motivation was "to manipulate the market and profit from a manufactured decline in our stock price." Nikola said that it retained an outside counsel, Kirkland & Ellis, for possible legal recourse and that it would work with the Securities and Exchange Commission to rebut the report.

The Friday slump brought Nikola shares to their lowest point since early August

The research firm added that several of Nikola's partners and investors "have been cashing out aggressively" through the year as its shares have surged on strong investor demand

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