Bale – who signed for Real from Premier League outfit Tottenham for a reported fee of £86million earlier this month – has made just one competitive appearance this season.
That was for Wales on Tuesday, as the 24-year-old came off the bench in his country's 3-0 FIFA World Cup qualifying defeat to Serbia in Cardiff.
Bale has battled a foot injury over the past month and doubts raged over whether he would be fit enough to feature for the Spanish giants at El Madrigal.
But Ancelotti confirmed on Friday that Bale would play, either from the start or off the bench.
Ancelotti said: "Bale will travel to Villarreal and will play.
"I'm not sure if he will start or come off from the bench."
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