Los Blancos have qualified for the last-16 stage of the Champions League, but were forced to settle for second spot in Group H after failing to hit top form.
The Madrid giants are also down in fourth position in La Liga - eight points off the league leaders Barcelona having dropped points in six of their 14 matches during the 2017-18 campaign.
Zidane has admitted that "there is a possibility" that Madrid will enter the winter market as they look to battle for three trophies in the second half of the campaign.
"There is a possibility we will do business. From January 1 to January 31, we can sign players. We'll have to see what happens, we have this opportunity every year and we always take stock and see what's possible," Zidane told reporters.
Los Blancos will find out their last-16 Champions League opponents when the draw is made on December 11.