The England midfielder suffered a thigh strain in the 4-1 victory over the Norwegians.
"It is a thigh strain. We need to wait but it could be one week," Benitez told liverpoolfc.tv.
Liverpool would not want to take any risks with Gerrard, however his presence against Liege would be welcome as the Reds attempt to take a big stride towards the group stages.
Benitez said: "It was another good work-out. It was a good game, with four goals for us and good play.
"But the players aren't 100 per cent yet - that would be difficult right now. The other team were fitter than us but you could see we were passing, pressing and the understanding between the players was better. I am really pleased with the result.
"Normally when you have quality, when you are playing well and creating chances, you will score goals."