A concerning disconnect may be emerging between equities and the market's measure of volatility, according to one portfolio manager.



Dennis Davitt of Harvest Volatility Management told CNBC's "Trading Nation" he's carefully watching the Cboe Volatility Index, widely considered the market's "fear gauge" as it measures equities' expected volatility over 30 days. Here are his reasons why.



• Stocks kicked off the week in rally mode across the board, with the Dow surging triple digits and going positive for the year, and the surging nearly 1 percent.



• Despite the market's strong showing, Cboe's VIX didn't decline as much as investors might expect; it was briefly positive on the session, falling a bit more than 1 percent by the market's close. This signaled market participants may not be buying into the market's rebound from recent lows.



• The lack of a major decline in the VIX during the rally, which is uncharacteristic, likely has much to do with global trade. If trade-related issues are not resolved with China, the market may very well pull back. At the moment, there's still uncertainty in the market that may not be fully reflected in the VIX.



• In the sessions to come, Davitt will be closely watching how the VIX moves in a rising market. If it fails to pull back meaningfully, this would be a bearish signal.



Bottom line: The market's gauge of volatility isn't falling as much as it typically would as stocks rally, which could be concerning for stocks, according to Davitt.