While most economists are debating whether the Federal Reserve will taper its quantitative easing (QE) in September or December, Steen Jakobsen, chief economist at Denmark's Saxo Bank, says the Fed will have to increase its QE next year.

The central bank is currently buying $85 billion of Treasurys and mortgage-backed securities a month.

A weak economy, in particular the struggling labor market, will force the Fed's hand, Jakobsen told CNBC.

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The drop in the unemployment rate to a 4 ½ year low of 7.4 percent in July hid the true jobs picture, he said.

"If you look at the reason why unemployment has come down, the participation rate has been a significant part of that. Basically, we haven't created necessarily more jobs, but less people have applied for jobs," Jakobsen said.

The labor force participation rate totaled 63.4 percent in July, down from 63.7 percent a year earlier. People who aren't participating in the labor force aren't counted as unemployed.

In addition, the weak economy in the first half of the year – growth averaged only 1.4 percent a quarter during the period – will depress future hiring, Jakobsen said.

Bill Fleckenstein, president of Fleckenstein Capital, also says the Fed will ultimately have to pull back from its tapering, because the economy can't withstand it.

"The thought that the economy is strong enough to demand this is ridiculous," he told CNBC. Still Fleckenstein isn't predicting additional QE like Jakobsen.

Declassified: ‘Financial War’ Could Wipe Out 50% of Your Wealth