Hiddink said recently: "Zhirkov plays a very modern game. He's capable of covering all the left side of the pitch alone.
"A player can only do this if he has brilliant technical skills and superb physical condition. He's a top-class footballer."
CSKA's Brazilian manager Zico also believes that the player has outgrown the Russian premier league, and his recent comments have hinted at a move to Chelsea.
He said: "Zhirkov is a player of such high level that in my opinion he would show all his real potential only playing in such a strong competition as the English Premier League.
"He would easily fit into Chelsea's first-choice team. I don't like to lose him but I won't stop his move to London."