It's only a matter of time before China lifts its ban on cryptocurrency exchanges, according to the entrepreneur behind what was once China's longest-running bitcoin trading operations.

"In this world, nothing is ever permanent," said Bobby Lee, CEO and co-founder of BTCC, which closed down its China-facing trading operations in September 2017 after a well-publicized government crackdown.

"One day I think it's possible they'll lift the ban, so called, and they might reinstitute it and license it," Lee told CNBC's "Squawk Box."

Still, Lee stopped short of offering a definitive timeline: "Frankly speaking, I don't know what kind of time frame that is, whether it's a few months, a few years or even a few decades, so it's hard to tell."

China cracked down on cryptocurrencies in September 2017, with authorities banning bitcoin trading and initial coin offerings after the People's Bank of China said such activities could pose major financial risks to the world's second-largest economy.