Billionaire hedge fund manager David Tepper, who was bullish on the market just a few weeks ago, said the coronavirus outbreak has changed the environment around stocks. Tepper, in an interview with Jim Cramer for TheStreet, said investors should be cautious until more is known about the virus. "You have to be careful, because it may be a game changer. So you've just got to be cautious," Tepper said. Tepper had told CNBC two weeks ago that he thought the market would keep climbing, saying "I love riding a horse that's running."