Wales international Bale has not played since the 3-1 win over Borussia Dortmund on September 26 due to a calf injury, while Navas has been struggling with a thigh problem since returning from the international break.
Neither player has resumed full training but Zidane believes both have a chance of featuring at Wembley on Wednesday.
"They're improving," Zidane told reporters. "We'll assess next week if they can play against Tottenham.
"They still haven't trained with the team and I still can't tell if you if they'll be in London. It depends how their injuries progress."
Concerns have been raised over security at Saturday's league game against Girona in Catalonia due to the ongoing political crisis, with the central Spanish government having imposed direct rule over the region after a vote to declare independence.
Despite the possibility of the game being postponed, Zidane does not expect any problems at the Municipal de Montilivi.
"We know it's a difficult pitch, we're expecting a tough game, like every weekend," he said.
"I'm only looking at the game. There's a lot of noise around the issue and I won't get into that. What matters to me is that we're going to do things on the pitch, nothing more."
The former France star also insists Madrid remain the best club in the world despite their inconsistent form this season.
"I think it's the best club in the world, I have no doubt about that," he said. "Last year we were the best team, with everything we won, but the following year you have to try to do the same.
"But as a club, for sure."