Wharton School professor Jeremy Siegel now believes 20,000 is in reach for the Dow, after earlier calling for the index to rise to 19,000 by the end of the year.

"Is it possible that we get another 5 percent in the month of December? Most definitely. That would probably get us to Dow 20,000 and 2,300 on the S&P," Siegel said Thursday on CNBC's "Futures Now." "I don't see the market stopping where we are right here."

Since Donald Trump won the presidential election, the has surged by nearly 5 percent while the S&P 500 is up more than 2 percent. In fact, the Dow has broken all-time highs seven times since the election.

"This looks like the early stages of a good equity move. Actually on Trump's appointments yesterday, if it weren't for bond yields going up, I think we would be up 200 to 300 points on the Dow," he said.

"I thought that was extremely reassuring and sets up a very good tempo and setting for the rest of this year and into the early months of the Trump administration."

Dow 20,000 would represent a further rise of about 4 percent for the index.