Tesla sheds $US5.4 billion after Elon Musk admits job stress getting to him

Shares of Electric car maker Tesla have tumbled about 9 per cent after CEO Elon Musk conceded in a newspaper interview that job stress may be getting the best of him.

Tesla shares closed at $US305.50 ($417.56) on Friday (local time), their lowest level since August 1, as analysts and business professors questioned whether the company's board should grant Mr Musk leave or even replace him with a more seasoned CEO.

The decline lopped $US5.4 billion off Tesla's market value.

In an interview with the New York Times Mr Musk admitted the past year had been the most "difficult and painful" of his career.

The newspaper reported that during an hour-long telephone interview Mr Musk alternated between laughter and tears, acknowledging he was working up to 120 hours a week and sometimes took Ambien to get to sleep.

"It's kind of bizarre," said Charles Elson, director of the corporate governance centre at the University of Delaware.

"It's a drama we shouldn't be watching."

Still, Mr Musk said in the interview he had no plans to give up his dual role as Tesla's chairman and CEO.