Investors are growing increasingly skittish about the stability of Masayoshi Son’s empire.

Son’s SoftBank Group Corp., one of Japan’s most indebted companies, had been chipping away in recent years at concerns about its ability to carry that burden. As the founder remade the telecom company into a tech investor, analysts reassessed the debt in terms of the value of SoftBank’s shareholdings, a gauge that had made its balance sheet appear more manageable.

But the coronavirus pandemic is threatening to undo that progress as it pulls down equity markets and triggers the worst sell-off in credit markets since the 2008 financial crisis. It’s sparked a dramatic surge in the price of insuring against defaults around the world, including SoftBank’s. The company’s credit-default swaps have spiked to the highest in a decade.