Significant conflicts of interest are embedded in these talks. Mr. Legere is separately renegotiating the terms of T-Mobile’s acquisition of Sprint, which cannot close until the case brought by the states is resolved. The merger deadline has passed, and Sprint remains a hobbled wireless business. T-Mobile’s shareholders are pressing for better terms with a lower price.

Mr. Legere could have a difficult time separating T-Mobile’s negotiations with Sprint from his talks with WeWork, given that SoftBank effectively controls both of those companies.

“The number of connections between these companies makes the situation highly problematic,” said Craig Moffett , a co-founder of the research firm MoffettNathanson.

A representative for T-Mobile declined to comment.

Mr. Legere may believe it is time for a new challenge. The next phase for T-Mobile is unlikely to be as exciting as the one in which it became the insurgent that telecom giants were forced to reckon with. He has also earned a fortune at T-Mobile. Between 2016 and 2018, his compensation packages totaled more than $110 million, according to securities filings.

Given the right financial incentives, Mr. Legere might be drawn to the challenge of turning around a company that is likely to remain in the spotlight. While there is growing demand for WeWork’s product — office space that offers more flexible terms than traditional leases — it has plenty of rivals that are in a better financial shape.

SoftBank’s $1.5 billion equity investment last month took its total investment in WeWork to more than $10 billion. It is planning to spend an additional $3 billion to buy WeWork stock from other shareholders, a transaction that would not put new money into the company. After that tender offer, SoftBank hopes to raise $5 billion for WeWork in a debt financing that would take the form of bond sales and bank commitments.

Investors and lenders putting up that money would have to be convinced that WeWork’s financial problems had been addressed and that the company had a future.