Still, he was defiant that WeWork was still a solid business, saying there would be a "hockey stick" recovery in its profits eventually.
The Saudi Arabia-backed Vision Fund, which is run by ex-Deutsche Bank banker Rajeev Misra, has invested $70.7 billion in 88 companies at the end of September.
Uber had pared back some of those losses since then, but fell to new lows on Tuesday after the company reported steep losses for the third quarter. The new standards will apply to future investments made by SoftBank, and the Vision Fund is in discussions about how it can adopt some of the measures, according to the Financial Times.
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SoftBank's first quarterly loss in 14 years comes after a terrible quarter for the tech companies backed by Son's venture capital funds, the $100bn (£77bn) Vision Fund and the smaller Delta Fund.
With increased market scrutiny over the path to profitability for many of its bets on unproven startups, Son was also more cautious about the timings of IPOs- an essential step to unlock capital to keep its investment juggernaut growing. But the outlook could be bleak, as startups like WeWork continue to struggle. "I am looking back with true regret about the mistaken investment moves that I have made". The firm leased four floors, or around 60,000 square feet (about 5,600 square meters), for nine years in the Hopewell Centre in August, one of the people said, asking not to be identified because the details are private.
"New executive leadership is evaluating our operations and assets across all geographies, including Hong Kong", a spokesperson for WeWork said in an email.
After Neumann left WeWork as part of an agreed $9.5bn rescue package by Softbank, Marcelo Claure, a senior SoftBank executive, was appointed to lead the troubled company.
"We are fully committed to improving the business and ensuring our long-term viability to the benefit of our landlords, members, and employees", the spokesperson said. The deals under review are at varying stages, from a preliminary inspection of promising properties to detailed talks.