Brian Kelly, founder of hedge fund Brian Kelly Capital and who is among those shorting the yuan, told Business Insider why that is.

He said:

Nobody cares because the bets have been placed in the derivatives markets and have been locked in for a while — which means any hedging has already taken place and there is not much the PBoC can do. They can threaten capital controls, but they already have them and they are not working and are unlikely to work even if tightened.

"I am short RMB via derivatives and I am in the camp that a 25%+ devaluation is likely in the next 12-ish months," he said.

A devaluation of that magnitude would require China to expend even more of its reserves to stabilize the currency. Barclays thinks that the country will, later this week, announce the largest single-month drop in its reserves in modern history.