The Spaniard has already held talks with chairman Steve Gibson and chief executive Neil Bausor over potential targets, but he will only move if he feels he can strengthen the squad he already has.
Karanka told the Northern Echo: "We are working towards January, but that is not just something that has started this week. We have been working ever since I joined the club.
"We want to have the best squad and in January we will look and if we decide we need some players, they will come.
"But we will only do something if we decide that the players who can come are better than the players that are already here."