China’s currency-swap lines with nations spanning the globe, designed to bolster the international role of the yuan, could backfire badly in a world crisis.

So argues Mansoor Mohi-uddin, a senior macro strategist at NatWest Markets in Singapore. The danger is that foreign central banks would exchange their currencies for yuan with the People’s Bank of China, then dump those holdings for dollars if a crisis hits, he wrote in a research note Friday.

“This would exert downward pressure on the yuan’s exchange rate against the greenback at a time when the PBOC would also likely be trying to shore up sentiment on its own currency,” Mohi-uddin wrote. Swaps “may be the yuan’s weakest link in a major financial crisis.”

Such an exchange would highlight how, though the yuan is now officially a reserve currency -- with the imprimatur of the International Monetary Fund -- its global appeal is well short of the dollar’s. China’s currency is used in 4.3% of global foreign-exchange transactions, against the dollar’s 88.3% share, according to the Bank for International Settlements.

China has set up currency swap lines with dozens of countries to grease trade and, if needed, to act as an emergency backstop. NatWest calculates the total as a potential 3.7 trillion yuan ($523 billion).