Bale, who became the world's most expensive player when he joined from Tottenham Hotspur for a fee of 100 million euros ($136 million) in the close season, missed Wednesday's 4-0 Champions League win at home to FC Copenhagen.
Ancelotti told a post-match news conference Bale was feeling down in the dumps but should be ready to return after next week's international break.
"We are not worried but he was not able to play today because he has a little problem," the Italian said.
"He had a scan, it didn't show anything special but he has just to recover his condition.
"Now we have the time because we have 15 days. I think that in 15 days he will be ready to play with us."
Bale is definitely out of Saturday's La Liga game at Levante and it remains to be seen whether he joins up with Wales for their World Cup qualifiers at home to Macedonia on Oct. 11 and away to Belgium four days later.
He played the second half of Real's 1-0 defeat at home to Atletico Madrid last weekend but was unable to train on Tuesday and was left out of the squad for the Copenhagen game.
He had been due to play his first game at the Bernabeu against Getafe the previous weekend but was withdrawn from the starting lineup after tweaking his thigh muscle in the warmup.
"It's normal that he is not happy because he wants to play," Ancelotti said.