All eyes are on Bale after his world-record move from Tottenham, but doubts over whether or not he will start against the Yellow Submarine exist because he has only played 32 minutes of football this season.
Ancelotti refused to confirm whether or not the Wales international will start at El Madrigal, but did say on Friday: "Bale will travel to Villarreal and will play.
"I'm not sure if he will start or come off from the bench."
When asked about where he would play, he added: "On the right hand side [of attack]."
Bale did not play for Tottenham this season before making his high-profile switch, and featured only off the bench for Wales.
The international break also meant his time with his new team-mates has been severely limited, with his first training session coming on Wednesday.
Nevertheless, Ancelotti is confident Bale can make an impact on Saturday.
"Bale came here without having a normal pre-season, but his condition is not bad. 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."
Bale will have a number of new issues to tackle at Madrid, including fitting in alongside superstars like Cristiano Ronaldo and dealing with the expectation that comes with such a large transfer fee.
Ancelotti though believes Tottenham could have received even more money.
"We have paid what the market dictated," said the Italian. "I'm sure that there were teams that would have paid more money to Tottenham than us, but the player decided he wanted to come here."
Bale said on Thursday he felt ready to play a part.
"Obviously I went straight away on international duty which probably wasn't the best but I've been back in the last two days now but the boys have been very nice to me and made me settle quickly and its just an honour to be here," said the 24-year-old.
"I feel good, I've been training last week with Wales. I've had two good sessions today.
"I got half an hour to 40 minutes' game time with Wales and I'm feeling good but obviously I'm a bit behind physically than everybody else but hopefully I can catch up as soon as possible.
"[Ancelotti] spoke to me but we have to wait until the match day to see whether I'm picked or not but hopefully I can get my fitness up straight away and get a place in the team."