Cresset Capital's Jack Ablin warns that June's big market gains could vanish in an instant on Wednesday afternoon.

With Day 2 of the Federal Reserve meeting on interest rates kicking off, the firm's chief investment officer believes the market is too optimistic a cut is ahead.

"There is absolutely no reason for the Fed to act," the $4.7 billion money manager told CNBC's "Futures Now" on Tuesday. "The markets are not going to like it."

But that doesn't meant a move won't come. According to Ablin, a less-than-fruitful G-20 summit in Japan at the end of next week could further derail market gains and provide the catalyst for the Fed to ultimately ease.

"We expect a disappointment in Osaka next week, and then the Fed to come back in July and lower rates," said Ablin, who predicts President Donald Trump and China President Xi Jinping won't agree to a meaningful deal there to end the trade war.

And that could set the market up for an even bigger rate cut.

"It's possible if disappointment in the equity market is big enough, they could come back with a 50-basis-point move in July," he said. "There's a difference between what the Fed should do and what the Fed will do. I actually don't think the Fed needs lower rates to ... boost the economy."

In the end, he predicts the Fed will cut to "calm down investors who are berating them, including the White House."