This last FIFA break didn't treat Gareth Bale very well. The attacker picked up a small injury in his gluteus muscle and was sidelined during Real's 0-5 win against Levante. Furthermore, he could miss Wednesday's Champions League match against Liverpool as well.
Bale could and would feature if this was a make or break game, but the coaching staff want him to heal this injury completely ahead of Saturday's decisive Clásico against FC Barcelona. It's true that Wednesday's visit to Anfield will also be an important game, but considering that Brendan Rodgers' side dropped points against FC Basel, Real Madrid still have a good cushion of points to work with. In addition to that, Real Madrid will not need Gareth Bale to harm Liverpool's shaky defensive system, so it makes sense to rest him one more match in order to have him ready for Saturday's make or break match.
Bale will almost surely be replaced by Isco, although James Rodríguez will be the one player staying on Bale's right wing, leaving Isco on the midfield.