The central midfielder is dealing with an Achilles injury that he suffered in May.
Fans were hoping he would be involved with the first team before the new year, but Lampard has quashed such suggestions.
"It's a long road," the Blues boss told a news conference.
"It's a difficult one for Ruben, because we want him back, we all know his quality. But it's going to be a while, it's going to be a while.
"I feel for him, because people will ask and the thing to say would be, 'Yeah, I'm really pushing on, it might be next week, it might be next month'.
"But I don't think that's quite the case. We need to let him get on with it. We're all supporting him here. There's no immediate news."