Dembele arrived in August as a direct replacement for Neymar after his world-record €222 million move to Paris Saint-Germain, but injury has curtailed his impact.
And, although the first Clasico of the Liga campaign takes place on December 23, Valverde does not feel tempted to risk him.
Speaking to reporters ahead of Sunday's visit of Deportivo La Coruna, Valverde told reporters: "Dembele is fine.
"He's started doing more things with the group this week, but he has not completed all the training.
"We're still on the same plan; we think that by January he can play. To do anything else would be risky."
Sergio Busquets goes into Sunday's match on four yellow cards, meaning another sanction against Deportivo will rule him out of the Clasico, but Valverde is not going to give it much thought.
"It is true that this is a circumstance to be taken into account," Valverde added.
"But you never know how the games can go. The three points are the same in both cases, plus a card can be given out to a player on the pitch, on the bench and in the tunnel."