"He likes a crazy challenge," said Sonnenfeld, who founded the nonprofit Chief Executive Leadership Institute.
Sonnenfeld's appearance on "Power Lunch" came after reports surfaced Monday that Legere was in talks with WeWork to become CEO of the troubled coworking company. The Wall Street Journal first reported the news.
It's not the first time Sonnenfeld has floated Legere's name in reference to WeWork. In September, he suggested on CNBC hat Legere would be a "perfect" replacement for Adam Neumann, who had just stepped down as CEO following controversy over WeWork's governance and valuation ahead of its expected IPO.
"He's been very good at revivals and resuscitations," Sonnenfeld said at the time. WeWork withdrew its IPO filing at the end of September.
In Monday's appearance, Sonnenfeld referenced Legere's tenure as CEO of Global Crossing after the telecommunications company was rocked by an accounting scandal in the early 2000s. He's also praised Legere's work at T-Mobile following AT&T's decision to drop its bid to buy the wireless provider.
"There is nobody else on the planet that has the same experience going into over-hyped environments and having the financial wherewithal to tease it out, but also the energy," Sonnenfeld said.
WeWork is in need of a leader to pull it out of its current crisis. SoftBank Group, struck a deal in October to take control of the company as part of a new $5 billion financing package. On Friday, WeWork said it would be divesting all "non-core" businesses.
"Wherever John Legere goes, that's the place to buy," Sonnenfeld said. "I thought that WeWork was circling the drain until this kind of news, but I would believe in WeWork with John Legere there."
Legere is a known commodity at SoftBank, which is the majority owner of Sprint and previously installed Marcelo Claure to run the mobile phone company. Last year, T-Mobile and Sprint agreed to a $26 billion merger, which has been approved by federal regulators but is still being opposed by various states.
Claure, who's now executive chairman of WeWork, once called Legere a "con artist" on Twitter, part of a heated spat between the two when they were rivals in wireless.
- CNBC's Annie Palmer contributed to this report.