The Israel international has been linked with a move away in January as Benitez faces the prospect of having to sell before buying.
But he told liverpoolfc.tv: "Yossi is a key player for us. Before, people had some doubts about him but we knew he has quality. He has game intelligence and he can change a game for us. When we don't have Gerrard on the pitch at the moment, Yossi can be a key player."