Not as bullish heading into 2015: pro

The stock market will not be as solidly bullish next year, one market pro told CNBC Monday, and that has him a little concerned.

"There's a little more risk in the market. The environment is not as clearly bullish as it had been. So we're getting a little worried," Mike Vogelzang, president and chief investment officer of Boston Advisors, said in an interview with "Street Signs."

A strong U.S. economy helped lift the market higher in 2014, with the Dow Jones Industrial Average up more than 4 percent just in the last five trading days. The S&P 500 has more than tripled from its March 2009 low.

Vogelzang said he believes the market could fall 8 percent to 10 percent next year.

"There's no question at some point during the year we'll have at least down period of 8 or 10 percent. It's almost inevitable in every year," he said.

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Bull sculpture market
Adam Jeffery | CNBC

While it would be a good strategy to buy that 8 or 10 percent dip, Charlie Bobrinskoy, vice chairman and portfolio manager at Ariel Investments, said that people get scared when the market drops.

"It's very hard to pull the trigger when the market is down 8 percent," he said.

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His advice is to stay pretty much fully invested.

"If you are going to keep money on the sidelines, keep it in cash because you are going to get hurt in fixed income," Bobrinskoy warned.

Most important, don't try to time the market.

"You are going to lose money if you try to come in and out," he said. "The right strategy is to generally be buying what others are selling, selling what others are buying."

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Both Vogelzang and Bobrinskoy believe the drop in oil prices has created some long-term opportunities in energy stocks.

"Long term, I believe that demand for oil and natural gas is going be higher five years from now than it is now. Production costs are going to be higher," Bobrinskoy said. "Therefore I think the price is going to be up long term."

However, short term is hard to predict, he noted.

Vogelzang said now could be a good time for investors to upgrade the quality of their holdings.

"If you can hold your nose and buy some of these things, start to accumulate," he said, noting that with the right names, long-term valuations look good.

—The Associated Press contributed to this report.