The cost of insuring against a default in SoftBank Group Corp's debt rose to hit the highest in two years and its bond yield also climbed as the slumping value of the Japanese conglomerate's tech investments unnerved investors.

The value of marquee portfolio companies have tumbled, with Alibaba and Didi Global dropping 35% and 64% respectively year-to-date, hit by China's crackdown on tech companies, the prospect of higher interest rates and war in Ukraine.

SoftBank CEO Masayoshi Son said last month "we will definitely be selling a good chunk of assets" as he pivoted after the collapse of the sale of Arm to a plan to list the chip designer.

However, with investors turning sceptical on money-losing startups, some analysts have questioned SoftBank's ability to sell down the portfolio in choppy markets and are floating the rising risk of SoftBank facing margin calls.

"The lack of profitability means there is no clear floor for share prices," Mio Kato, analyst at LightStream Research, wrote on Smartkarma. "We are thus unconvinced about their ability to monetise holdings in any significant manner," he wrote.

SoftBank did not immediately respond to a request for comment.

SoftBank's 5-year credit default swaps rose by around 25 basis points on Wednesday to a two-year high, data from IHS Markit showed. The yield on SoftBank's unsecured eurobond maturing in 2025 closed at 6.767% on Tuesday, the highest in almost two years. It was around 3.1% at the end of last year.

"Debt investors are generally more conservative than equity investors, but if they're worried then equity investors probably should take notice," said Redex Research analyst Kirk Boodry.

SoftBank shares are trading at their lowest level in two years. Shares were flat at 4,273 yen on Wednesday morning. The group's share price collapsed to below 4,000 yen in the early days of the pandemic as valuations slid, triggering a record buyback funded by asset sales.