Wharton School finance professor Jeremy Siegel thinks the seemingly endless series of good news for the bull stock market has come to an end and investors will face a wall of worry.

Surging interest rates are a “major impediment” for the fourth quarter, he recently warned CNBC.

“It’s psychology. Look at all the potential negatives,” he said, citing the U.S. government deficit of $800 billion and the Federal Reserve selling Treasury bonds as it unwinds it balance sheet. Also add in the lingering U.S.-China trade tariff squabble in which the Chinese haven’t been buying Treasurys.

“Not a bear market, It’s just that the good news is out there [in the market]. I don’t see any more ... good news,” he added. “I see potential risks,” he said.

“That sort of psychology is going to creep into the decisions that’s going to make this quarter a difficult one,” Siegel said.

However, he said any type of market selloff is healthy to remove proverbial dead wood for investors.

The S&P 500 was little changed on Monday as concerns mounted about the impact on China’s economy from trade tensions between the United States and China.

Beijing announced a steep cut in the level of cash that banks must hold as reserves, aimed at lowering financing costs and spurring growth amid the trade spat between China and the United States. In Monday’s trading session, the first trading session for mainland China investors since the two countries imposed additional tariffs on each other’s imports, both Chinese stocks and the yuan slid.

The dollar rose slightly in response to the turmoil in Chinese markets. Some investors have grown concerned that the stronger dollar, along with mounting tariffs, could hurt large U.S. exporters as their products become more expensive for overseas customers.

“These are things that could derail the good momentum in the economy right now,”  J.J. Kinahan, chief market strategist at TD Ameritrade in Chicago, told Reuters.