The Welshman was withdrawn at half-time in Real's 2-0 La Liga victory over Granada on January 25 due to a leg injury, and has missed the past three matches in all competitions.
He was missing for the comprehensive 3-0 triumph over rivals Atletico in Wednesday's Copa del Rey first leg at the Bernabeu.
Bale has struggled with several injuries in his debut season at the club, and there were fears he could be set for a prolonged absence with his latest issue.
The 24-year-old's availability is even more vital for Real as Cristiano Ronaldo is set to miss the next three Liga matches after being sent off against Athletic Bilbao.
Ronaldo was able to feature against Atletico as the ban does not apply to the Copa del Rey, affording Ancelotti the chance to give Bale more time to recover ahead of Saturday's encounter with Villarreal.
"Bale is doing well but I decided to rest him because Ronaldo was available," Ancelotti said. "I'm sure Gareth Bale will play in Saturday's match.
"Nobody is happy that Cristiano Ronaldo is suspended. It's not normal to get a three-match ban for what he did."
Real put one foot in the final of the Copa del Rey, as own goals from Emiliano Insua and Miranda sandwiched Jese Rodriguez's strike.
But Ancelotti warned Atletico will pose a dangerous threat in the return leg at the Vicente Calderon.
"It's a good result. The match was really good but we have to be careful because there is another match on the way at Vicente Calderon," he said.
"We did well in the first match. It won't be easy because Atletico will try everything to get into the final. We have to get ready for that match as we did for tonight and keep going."
