Bale picked up a calf injury in the first leg of Real's Champions League quarter-final meeting with Bayern Munich on 12 April, missing last Saturday's La Liga victory over Sporting Gijon and the return leg against the German champions on Wednesday.
The Wales international returned to training the following day, coming through unscathed in a final training session on Saturday morning. Reports in Spain have suggested Real's medical staff are wary of the injury, however, fearing a premature return against Barcelona could aggravate the problem.
But the final decision now rests with Zidane, who confirmed the former Tottenham Hotspur star will be in his 18-man squad – but stopped short of revealing whether he will start or not.
"Bale will be with us tomorrow and you will see if he starts," Zidane told a press conference on Saturday. "We are focused on what we are going to do tomorrow and what we want is to try and do our best to win."
Real were boosted on Friday by the return of Raphael Varane to training. The France international suffered a recurrence of a hamstring injury at the beginning of April, limping off just 11 minutes into a 3-0 win over Alaves, but was able to train with his teammates again on Saturday.
AS report however Sunday's derby will come too soon for the 23-year-old, who could be available for upcoming league matches against Deportivo or Valencia.
Pepe meanwhile is also ruled out to face Barcelona due to a rib injury but could be back for the first leg of the Champions League semi-finals with Atletico Madrid on 2 May.
Barcelona come into the fixture with their own selection headache, namely around the status of Neymar. The Brazil international had been set to serve a suspension on Sunday, although the Catalan giants still hope to have it overturned having taken their appeals to the Court of Arbitration for Sport.