SOPA Images/Getty ImagesA key US license allowing Russian yuan transactions is set to expire mid-October.That could make Chinese banks more hesitant to deal in Russia, worsening Moscow's yuan shortage.Russian banks have already nearly depleted their stash of yuan, Reuters reported last month.It may about to be way harder for Russia to get its hands on Chinese yuan.That's because a key license from the US Treasury that permits transactions from some of Russia's financial institutions is about to expire.