"We just want Disney to embrace the future and go all in," Greenfield said Monday on CNBC's "Fast Money." "There's no putting your toe in the water and playing the streaming game."
The Walt Disney Company announced last summer that it would pull all of its content from Netflix and develop its own content with two streaming services: an ESPN video streaming service that would launch in 2018 and its own Disney brand direct-to-consumer streaming service in 2019.
But Greenfield said the legacy media company's methods are off, as Disney tries to expand across multiple platforms, including original content, movie theaters, theme parks and multi-channel cable packages. Disney's cable packages range from $80 to $100 a month, far higher than Netflix's $13.99 premium package, the most expensive the company offers.
The key is to shake up the old business model, Greenfield said.
"They should be launching day and date with all of their best content," he said. "Not trying to create incremental content."
"Going for it means disrupting earnings and taking a step down in earnings," Greenfield said.
But the analyst predicts Disney won't, because "they basically want their cake and to eat it too."
"They don't want to disrupt their legacy businesses while they build the new business," Greenfield said. Disney has a market cap of more than $150 billion.
Meanwhile, competition looms from other media companies, most notably Netflix.
The streaming giant has become a powerhouse of its own, with a market cap exceeding $130 billion. So far this year shares of Netflix stock are up 64 percent compared with the broader S&P 500's 2 percent increase. Even price increases last October for new customers, the first time in two years, didn't deter new customers. Netflix added 24 million members in 2017, 8.33 million in the fourth quarter alone.
Greenfield pointed out that the biggest criticism of Netflix is that the company doesn't make any money, with a $2 billion negative cash flow.
But "that's the pushback. Disney would have to meaningfully step back in earnings," he said, in order to grow with current consumer trends.
But acquiring a legacy media company, Greenfield warned, comes with problems of its own, such as other distribution deals that are already in motion.
"If I'm Disney, what should I be doing with $80 billion of capital?" said Greenfield, who called Disney "the best content creator on the planet." "I should be investing in the future. If they want to put money to work they should be building."
"If Disney just spent and created its new content directly for the consumer, they could win," he said.