Cramer: This is what Wall Street fears about Fitbit

CNBC's Jim Cramer said Tuesday Fitbit's stock is dropping because it just raised one big concern for investors.

"Is this the wellness tool of the future or is it GoPro? And that's what everyone fears; that it's just another GoPro," Cramer said on "Squawk on the Street."

GoPro shares have lost nearly 70 percent of their value in the last year. GoPro did not immediately respond to a CNBC comment request.

Fitbit reported third-quarter earnings per share of 24 cents and revenue of $409 million on Monday, while analysts expected the company to post EPS of 10 cents on revenue of $352 million.

However, the company said in another statement that "certain stockholders" are proposing a secondary sale of 14 million shares.

"Until you heard about the big secondary … the stock was screaming because the number was not just better than expected, it was maybe the best beat of any expectations in the quarter," Cramer said.

Fitbit's stock was sharply lower in early-morning trading.

DISCLOSURES: Cramer's trust did not own shares of Fitbit or GoPro when this article was published.