The Russian rouble weakened slightly against the U.S. dollar and the Chinese yuan on Friday ahead of the expected central bank rate hike. The central bank is widely seen lifting the key interest rate by 100 basis points to 20%, which would provide support for the Russian currency. Western sanctions have shifted trade in dollars and euros to the over-the-counter market, making the yuan the most-traded foreign currency in Russia. Brent crude oil, a global benchmark for Russia's main export, was up 0.5% at $74.69 a barrel as Middle East tensions continue.