Russian bankers have relied on the rouble bond market as a risk-free option for more than a year now.

Thanks to central bank stimulus measures, Russian banks that are too wary to lend directly to corporates, have now found that they don't have to. The stimulus allows them to reap risk-free returns of 130-170 basis points on rouble paper, simply by borrowing money on the market and buying up central bank bonds.

But, whilst the system has worked well for Russian corporates – which have been able to issue $23.1 billion in rouble debt this year thanks to falling borrowing costs – there are concerns that this will negatively affect Russia's financial system.

Economists at Moscow investment bank Troika Dialog, say that the central bank is not helping by offering banks “nice, risk-free” bond offerings, giving banks ample returns “for doing nothing but simply borrowing on the market [and] inflating [their] balance sheet.”

Banks will buy the central bank bonds but use them as collateral simply to borrow more on the market the next day.

“Statistics indicate that the system is awash with liquidity, and the Central Bank can again be blamed for provoking excessive money creation,” Troika says.