The world-record signing was in line to make his home debut for Real in their 4-1 win over Getafe on Sunday, but was not included in the 18-man squad after feeling discomfort in his leg during the warm-up.
Instead, Isco started in his place and produced an excellent performance, scoring Real's third goal after quick thinking from Cristiano Ronaldo, who scored two of his own.
Pepe had earlier cancelled out Angel Lafita's opener for Getafe, but attentions turned to Bale after the match and Ancelotti believes the Welshman should return against Real's city rivals after sitting out Wednesday's match at Elche.
"Bale had a small problem when he was warming up. It's not an injury. He just didn't feel comfortable," the Italian said.
"He was disappointed because he was very excited to play.
"I don't know if he can play on Wednesday because it's difficult for a player to be ready in 3 days. (But) I think he will be ready for Saturday's match.
"We are working to improve Bale's fitness because he didn't have a good pre-season."
Ancelotti went on to speak about Isco and Angel Di Maria, praising the former’s overall talent and the latter’s excellent work ethic.
"Isco arrived here with a lot of personality. It's difficult to play here (for Real Madrid) but he is very talented," he added.
"Di Maria is a unique player. He works a lot for the team, he defends and assists the strikers too."
