(Reuters) - Citron Research has taken a short position in MicroStrategy, the company said in a post on social media platform X on Thursday. Shares of the largest corporate holder of bitcoin were last down more than 8%. They opened sharply higher on a rally in bitcoin prices, which were nearing $100,000 after crypto-friendly Donald Trump's victory in the U.S. presidential election. "Now, with Bitcoin investing easier than ever (ETFs, $COIN, $HOOD), $MSTR's volume has completely detached from BTC fundamentals," Citron wrote while stating it was bullish on bitcoin. "Much respect to (Michael Saylor), but even he must know (MicroStrategy) is overheated." MicroStrategy did not immediately respond to a Reuters request for comment. Under Executive Chairman Saylor, the company has raised capital all through the year to acquire more bitcoin, with a $2.6 billion debt offering on Wednesday the latest. Its shares have surged more than 600% so far this year.