Superstar economist David Rosenberg said stocks might plummet below their March lows thanks to the economy’s weakness.

That would mean a drop of more than 24 percent for the Standard & Poor’s 500 Index from Tuesday’s close.

"Could we see a new low? Who's to say that we couldn't?" Rosenberg, chief economist at Gluskin Sheff, told CNBC.

Stocks are just half-way through a bear market that could last another nine years, he said.

The big picture is that “we are into an epic post-bubble credit collapse,” Rosenberg said. “The transition to the next cycle is usually fraught … with double-dip risks, lingering deflation pressures and economic and financial fragility.”

Rosenberg is particularly pessimistic about employment. We’ve already lost 9 million full-time jobs, he said.

That means the real U.S. unemployment rate, including workers pushed to part-time, is 16.5 percent, he said. The official unemployment rate is 9.5 percent.

The official rate will “easily” surpass the post-World War II high of 10.8 percent, as job losses continue over the next several years, Rosenberg said.

“It’s going to be the mother of all jobless recoveries, when we actually get to the recovery,” he said.

Other experts see trouble for stocks, too.

"The markets are becoming more realistic," Subodh Kumar, global investment strategist at Subodh Kumar & Associates in Toronto, told The Associated Press.

"We can't snap our fingers and have recovery."