The biggest institutional investors have been shedding Apple stock

Apple is going to need to wow major investors at its event Wednesday if it wants to turn around a trend in which the biggest global funds have been offloading Apple shares.

New data from eVestment show that institutional investors across a variety of groups sold Apple in the second quarter. The drop in Apple's ownership was bigger than any other major stock.

Apple may still be the third most widely held stock in eVestment's database, but it's now only held by 20.42 percent of all funds, a drop from 20.83 percent a quarter ago. That contrasts with increases in ownership for other tech companies like Facebook and Amazon.

The data above focus on specific types of funds: growth equity, value equity, and core equity (a mix between growth and value). Apple was the single most sold stock in two of those three groups.

"Some investors and asset managers may be starting to believe Apple's big growth days are behind them," said eVestment's Mark Scott. "Some of its latest product releases have had changes and improvements that to many industry watchers and consumers seem more incremental than revolutionary." EVestment's figures covers over 65,000 institutional portfolios, giving the company deep insight into their trading behavior.

Scott said the recent lack of amazing product launches could be a problem for institutional investors, "and something that's making them rethink the position of Apple in their portfolios."

Meanwhile, JJ Kinahan of TD Ameritrade told CNBC's "Closing Bell" on Tuesday that retail traders have actually been buying Apple's shares in August.

That's one reason Wednesday's product announcement is going to move markets. Shareholders big and small were watching, ready to trade.

But while Wednesday's event was under way, Apple's stock was flat, down 0.35 percent.