Investors will be motivated to sell their stocks and shift to the S&P 500 once the hits 20,000, CNBC's Jim Cramer said on Tuesday.
U.S. stocks extended gains Tuesday putting the Dow within striking distance of 20,000, a milestone it's never reached. Cramer said that the index crossing that level could ignite a selloff.
"I think people say that it's overdone," Cramer said. "Remember, there's always the wise guys who say, 'Now it's on the front page, so I've got to sell it.' I think it brings out some sellers."
He continued: "But nothing for real, because we still haven't heard from a lot of the companies — We don't know what IBM is doing. We don't know how Wal-Mart is doing. Remember, in five weeks, we will know."
Many companies are expected to report their quarterly results in the coming weeks.