Former Fortress hedge fund manager Michael Novogratz told a conference Tuesday that the digital currency market will be a wild roller coaster ride full of froth and shady behavior.

"I think this [crypto] is going to be the biggest bubble of our lifetimes by a longshot," he said at the CoinDesk Consensus: Invest conference in New York. "To be fair, this is a bubble and there's a lot of fraud mixed in. We look at tons of projects. And some get funded, and they literally look like Ponzi's. There's a lot of froth and fraud in something that's exciting as this."

Novogratz's comments come a day after he gave an aggressive price forecast for bitcoin next year.

"Bitcoin could be at $40,000 at the end of 2018. It easily could," Novogratz said Monday on CNBC's "Fast Money." "Ethereum, which I think just touched $500 or is getting close, could be triple where it is as well."