Business sentiment among Korean companies is cooling once again as the U.S. and European economies show signs of slowing down.

According to the Bank of Korea on Tuesday, the business sentiment index among manufacturers fell to 98 points in August, down five points from July and into negative territory.

A BSI reading of less than 100 means pessimists outnumber optimists about future economic conditions. After peaking at 103 points in April, the BSI stayed above 100 until July.

The August BSI among major conglomerates fell seven points while the index among key exporters slipped eight points. The BSI for small and mid-sized companies dropped five points over that period, while the index for manufacturers catering to domestic demand fell two points. The statistics triggered concerns over the future performance of the Korean stock market.

The Financial Times of London on Monday said there are chances of a "stock market bubble" forming in Korea, whose bourse has performed well recently. Large firms' brisk performance drove the Korean stock market rally in the first half. But the FT predicted it will be hard for them to continue their earnings surprises in the second half and added a bubble will begin to form in the KOSPI once it goes beyond 1,800 points.