The Wales international winger, who moved to the Spanish capital from Tottenham for €100 million last week, has only played 32 minutes of football this season due to injury.
Ancelotti said: "Bale will travel to Villarreal and will play.
"I'm not sure if he will start or come off the bench."
When asked about where he would field the 24-year-old, he added: "On the right-hand side [of attack]."
Ancelotti feels the Welshman will bring welcome "enthusiasm" to proceedings nevertheless.
"Bale came here without having a normal pre-season, but his condition is not bad," he added. "He will travel tomorrow, and he will play. He has no injuries, he is excited and very motivated.
"He's arrived full of enthusiasm and he is very happy to be at the team he wanted to join. He is a humble player who likes to be with his team-mates. He fits in well with the squad."
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