Eden Hazard sustained a thigh injury in training on Friday, meaning Bale could even start against Celta following a turbulent summer for the Welshman.
Zidane was keen for Bale to be sold but Madrid cancelled a deal with Chinese club Jiangsu Suning while the winger's salary of around 18 million euros a year has proven too high for other interested clubs.
Bale is also eager to stay at Madrid, where he has a contract until 2022, and is not interested in moving to Paris Saint-Germain, despite suggestions he could be included in a bid for Neymar.
"It looked like he was leaving and now he's here with us, that's it," Zidane said.
"The dynamic changes and things change and now I'm going to count on him like everyone else. I said it a short time ago, I'm going to count on all the players that are here."
Zidane left Bale out of his squad for three consecutive pre-season friendlies but the 30-year-old returned for the last game against Roma, when he came off the bench in the second half.
The transfer window in Spain closes on September 2.
"He has a contract, he's an important player and I hope all the players want to make it difficult for me to pick the team," Zidane added.
Zidane had promised wholesale changes this summer and his first press conference of the season was dominated by questions about the transfer window.
He refused to be drawn on a move for Neymar, insisting: "Neymar is not a Real Madrid player. We are interested in the players that are here."
And on the failed attempt to buy Paul Pogba from Manchester United, he said: "Paul is a player for Manchester United and we have to respect that. Here we are thinking about the game tomorrow."
But Madrid's failure to sign Pogba and sell either Bale or James Rodriguez means the club's president Florentino Perez has perhaps not dRead More
