The Wales forward is Madrid's second-top scorer behind Cristiano Ronaldo this season but has become dispensable in the biggest games, with Zidane starting without him in both of their Champions League last-16 games with Paris St Germain before leaving him on the bench in the quarter-final first leg at Juve.
"I understand that he is not in a good mood, that's normal," Zidane told a news conference on Saturday, ahead of Real's La Liga game against city rivals Atletico Madrid on Sunday.
"Players want to play in every game. We know what a good player he is and what he has done. I have to take decisions but if he doesn't play two games it doesn't mean anything. I still think he's an important player."
While his fellow substitutes wildly celebrated Ronaldo's outrageous bicycle kick goal against Juventus, Bale barely reacted.
He also did not stay on the pitch with the rest of his team mates to salute their fans after coming on as a substitute in their 3-1 win at home to PSG in February, which was interpreted in the Spanish media as a sign of his anger at not starting against the French side.
The Wales forward had a dream first campaign at Real following a then world-record 85.5-million-pound move from Tottenham Hotspur in 2013, scoring in the Champions League and King's Cup final victories over Atletico Madrid.
He played another key role in Real winning the 2016 Champions League but his influence has waned in the last two seasons, not helped by a serious ankle injury last campaign and repeated muscle problems.
Bale has remained injury-free since returning to action in December but has fallen behind Spain midfielder Isco in the pecking order in the biggest games, while Lucas Vazquez and Marco Asensio were preferred by Zidane as substitutes in Turin.
"He didn't warm up because someone has to make these decisions and another player came on but that is in the past now and we have another game tomorrow and he's as prepared as anyone else," added Zidane.
Reports in the Spanish media indicate Bale will be sold in the summer, although Zidane said he expected the forward to remain in Madrid, without offering any guarantees.
"My sensation is that he will stay but I don't know everything that will happen," added the coach.
"He won't lose any motivation, he's like the rest of the squad. It's my job to try and make sure he plays as well as always. He's an important player but others played against Juventus and did very well. That's football."