A Bloomberg report said Vanguard - which manages $ 6.2 trillion in assets - chose not to buy the latest Saudi bonds two weeks ago.
According to the report, Saudi Arabia - the largest oil exporter in the world - is emerging as the most vulnerable after the collapse of crude oil prices this year.
When it comes to the Gulf, Vanguard Asset Management buys Abu Dhabi and Qatar bonds and avoids Saudi bonds.
"Saudi Arabia still has a lot of foreign exchange reserves and assets to deal with the difficulties, but we think it is less powerful than Abu Dhabi and Qatar," said Nick Eisinger, co-chair of Vanguard Emerging Markets.
All economies in the region are under pressure from the outbreak of the emerging Corona Virus pandemic on oil demand. Brent crude prices fell to $ 25 a barrel, 60% less than at the end of last year.
Saudi Arabia needs a price of $ 76 to balance its budget this year, which is higher than the parity price in Abu Dhabi, which is less than $ 70, and twice the price of Qatar, which is approximately $ 39, according to the International Monetary Fund.
Saudi reserves fell by $ 27 billion in March, the largest figure on a monthly basis since at least 2000.