Ousted former Nissan boss Carlos Ghosn has said the future of the Japanese car giant is in doubt.
Mr Ghosn told the BBC that the struggling firm's results and the drop in its share price worried him.
He added that if Brexit were to affect Nissan's competitiveness in the EU, the future for its Sunderland plant would be "bleak".
Mr Ghosn recently skipped bail in Japan, fleeing to Lebanon, after being charged with financial crimes.
"I'm worried about the future of Nissan, period," Mr Ghosn said. "I'm not very optimistic about the future of the company, knowing the results, and the management, and everything that is taking place."
In November last year, Nissan reported that its half-year profit had slumped by 70%. It also cut its full-year forecast to an 11-year low.
This followed an announcement in July 2019 that it would cut 12,500 jobs after a collapse in quarterly profit.
The car giant has been hit by falling sales and a strong yen, while Mr Ghosn's ousting was followed by internal turmoil.
Mr Ghosn, who became known as "Le Cost Killer" after radically overhauling Renault's loss-making South America division, said Nissan's management "don't seem to worry about their bottom line, they don't seem to worry about their business, they seem to be more worried about investigation and supporting prosecutors than anything else".
Mr Ghosn fled to Lebanon on 29 December and gave a news conference there on Wednesday.
He said he had been a "hostage" in Japan, with a choice between dying there or running.
Japanese prosecutors hit back, saying Mr Ghosn's allegations "completely ignore his own conduct, and his one-sided criticism of the Japanese criminal justice system is totally unacceptable".
Mr Ghosn said another point of concern for Nissan was its drop in share price.
"Shareholders don't usually go to protest, they vote with their feet, they just sell," he said, adding that Nissan shares had dropped more than 37% since his arrest, while car industry shares had risen 12% in the same timescale.
He added that the future of Nissan's Sunderland plant in the UK depended on the firm being able to maintain its competitiveness in Europe after Brexit.
"If Nissan loses competitiveness in Europe, then, well, the future of Sunderland is bleak," he said.
In response to Mr Ghosn's comments, Nissan reiterated a statement it published on Tuesday: "The consequences of [Mr] Ghosn's misconduct have been significant," it said.
"In addition to his prosecution in Japan, the US Securities and Exchange Commission concluded that [Mr] Ghosn's conduct, including his schemes to under-report his compensation, was fraudulent.
"Investigations in France concerning possible misconduct are still ongoing. Nissan will continue to do the right thing by co-operating with judicial and regulatory authorities wherever necessary."