"We are in the sixth year of a recovery; imbalances can emerge as a result," Bloomberg quoted Greenspan as saying.
"Ten-year recoveries have been part of a much broader global phenomenon," Greenspan said in the interview.
He said the historically normal business cycle was much shorter and was likely to be this time, the news agency said.
Greenspan's outlook contrasts with the views of his successor Ben Bernanke, who told Congress last week that the economy may strengthen this year. Bernanke's assessment helped steady stocks markets after a plunge the day before, Bloomberg said.