Wharton professor Jeremy Siegel says there is 'more pain to come' for stocks as the bottom is likely still months away

• Jeremy Siegel expects more downside ahead for US stocks and expects the bottom to be months away.
• "I think there's more pain to come," he told CNBC. "I certainly wouldn't be surprised that the Nasdaq go into the bear market territory and the S&P."
• The Wharton professor also said he expects the Fed to raise interest rates eight times this year.
• Sign up here for our daily newsletter, 10 Things Before the Opening Bell.

Wharton finance professor Jeremy Siegel gave a bearish stock market outlook Monday, predicting the downturn's bottom is still months away.

The comments came as the benchmark S&P 500 joined the tech-heavy Nasdaq in correction territory as it is now down more than 10% from its high. 

"I think there's more pain to come," he told CNBC. "I certainly wouldn't be surprised that the Nasdaq go into the bear market territory and the S&P."

In fact, a further 10-15% slide for the Nasdaq would "not be unusual," he said. The Nasdaq fell into a correction last Thursday, slipping by 14% from its November all-time high. On Monday, it was nearly 17% below that high, nudging it closer to the 20%-decline threshold for a bear market.

US stocks have been seeing immense selling pressures as investors brace for the Federal Reserve to sharply tighten monetary policy to tame inflation that's near 40-year highs.

"I think the Fed has got to be more aggressive," he told CNBC. "That's going to be the trigger that's going to finally cause the market to bottom probably at the end of the first or second quarter of this year."

The central bank will release its first policy decision of the year on Wednesday, when it is widely expected to signal the start of rate hikes in March. 

Siegel said he expects the Fed to raise interest rates eight times this year — double that of other Wall Street commentators. The renowned author of the investment book "Stocks for the Long Run," also expects Fed Chair Jerome Powell to be more hawkish in this policy meeting. 

"The Fed fund's rates are going to probably be at 2% by year-end," he said. "The market has not completely digested that yet." 

Still, he isn't all that pessimistic. The professor said there is a "very good chance" the benchmark index will be up by the third and fourth quarters. For now, he said, "the next six months are going to be tough for the market."

"When a bear market comes, it doesn't spare the good stocks or the bad stocks. I mean, they all go down," Siegel told CNBC. 

Given this environment, he offered investors some advice:

"I would wait if I had cash to deploy and I would underweight those technology stocks," he told CNBC. "I would prune those that are on the more speculative side, push towards those that are more on the value side that are earning, that are giving dividends."