Speaking at the Kase Learning Short Selling Conference in New York, Stanphyl Capital Partners founder Mark Spiegel criticized Tesla's financials and said they are "worsening" under heavy competition from luxury automakers.

Tesla Chief Executive Elon Musk on Wednesday raised eyebrows by cutting off analysts' questions about capital requirements after the company reported a record loss for the first quarter.

Tesla shares tumbled as much as 8 percent on Thursday as investors worried about the fallout from Musk's behaviour on the earnings conference call.

Spiegel began his presentation at the private investment conference by saying "That was the funniest friggin' call."

He then devoted his allotted 15 minutes to disparaging Musk and arguing that Tesla has no protective moat to give it a competitive advantage, even when it came to technology.

Spiegel is not the only one betting against Tesla, with the stock listed as the biggest U.S. equity short, according to financial analytics firm S3 Partners.

Tesla's stock price dropped to $283 on Thursday, down from a record of $389 reached in September. The retreat comes as a relief for some short-sellers after the stock climbed for much of 2017.

The latest share move wiped out Tesla short-sellers' 2018 losses, bringing year-to-date paper profits to $683 million (£502.41 million), according to S3 Partners.

Prominent funds betting against Tesla include Jim Chanos' Kynikos Associates LP and David Einhorn's Greenlight Capital.

(Reporting by Svea Herbst-Bayliss; Editing by Meredith Mazzilli)