Blackstone chief executive and co-founder Steve Schwarzman believes there is little reason to be hopeful about the prospect of a trade deal coming to fruition before the end of the month.

On Tuesday, President Donald Trump said he and Chinese President Xi Jinping would have an "extended meeting" at the G-20 summit in Osaka, Japan scheduled for June 28-29.

The face-to-face meeting was welcome news for financial markets, with stocks jumping as skittish investors took comfort in a development aimed at resolving the ongoing trade war between the two economic superpowers.

When asked Wednesday whether he was optimistic something could be signed at the G-20 meeting, Schwarzman replied: "I think that's extremely improbable because there has been almost nothing happening since May when the discussions ended."

The chairman and CEO of private equity giant Blackstone, which has over $500 billion in assets under management, told CNBC's "Squawk Box Europe" that Trump and Xi must first decide "how far they are willing to go conceptually" before letting senior trade officials work out some of the finer details.

"I think the expectation of signing something is not on the table," he added, but suggested that the G-20 discussions could lead to something in the future. "This (meeting) would be a restart, you know, with a senior framework, and then you'd see what happens."