The Frenchman, who is now assistant coach at Madrid, has also claimed that Bale could emerge into a better player than he was during his time in Spain.
"Nobody at Real Madrid was ever worried about the form of Gareth, we knew exactly what the quality of player was that we had brought," Zidane told the Daily Mail.
"The only worry I have about him now is that he goes on to be a better player for Real Madrid than I was! He is the complete attacking player - he can score, he has pace, he can create, and has we have seen he is a specialist from set pieces.
"We knew all this though - that is why we spent so much effort making sure he was a Real Madrid player this summer. I think he can still get even better - and he knows my door is always open to him when he needs advice - and I look forward to being part of his development - as he has everything to become the best player in the world."
Bale scored his first treble for Madrid in their 4-0 win over Real Valladolid at the weekend.