31-year-old Gareth Bale only started 14 games in all competitions in 2019-20 and has played twice since football in Spain restarted in June.
“It was a personal conversation I had with him. He preferred not to play,” said Zidane.
“The rest remains between me and him but he said he didn’t want to play.”
Gareth Bale decided not to travel to Manchester because he knew he had no chance of involved in the match.
Manchester City won 2-1 in the first leg in Spain in February just before the COVID-19 pandemic caused the competition to be stall for almost five months.
The winner will play either Lyon or Juventus in the quarter-finals.
Is Bale’s future lies in Madrid, Zidane said: “I don’t know. Now he is a current player at Real Madrid. That has not changed. He is our player.
“I respect that and I respect him, like everyone else.
“He preferred not to play. That is the only thing I can tell you. The rest of us are all here, preparing for the game. The only thing we are concentrating on is the game.”