It means the midfielder will be fresh for the El Clasico this week at Barcelona.
Zidane explained, "I don't know how many games Casemiro's played... 21? I had to give him a little rest. Casemiro wasn't expected to play in this match. All three did very well.
"Because on top of this, Casemiro has played a lot of matches and I'm very happy with how we did, the whole team. We drew the game but I think we deserved a little more today."
He added: "At the end of the day, we've picked up an important result because it's crucial to keep taking points. Our first half was fantastic, we had chances to score goals for the first 35 minutes.
"How we set up, with (Toni) Kroos, (Luka) Modric and (Fede) Valverde switching positions with ease, we controlled the game well. They came into it more in the second half, but it was important to pick up the point today."