Cash-flow issues continued to plague small-business owners in September, dragging their confidence in the U.S. economy to a record low, Discover reported Monday.

Among 1,000 owners surveyed nationwide, 46 percent reported cash-flow problems within the past 90 days, up from 41 percent in August and 35 percent in July.

As a result, Discover's monthly small-business confidence index fell below its benchmark level of 100 for the first time since being launched in August 2006, dropping to 99.2.

"Cash-flow constraints are a very tangible sign that can move the index," Sastry Rachakonda, director of Discover's business credit card, said in a statement. Owner confidence has been fading for the past few months, he added.

Despite the downturn, 36 percent of respondents said that would spend more on business development in the month ahead, up from 34 percent in August.