If the cat is showing signs of hunting the Gecko, then keep them apart would be my advice. Cats see all small animals as a potential meal unless they have been together since the cat was a kitten. Our Dexter is very gentle with my two lizards. he will pat them gently on the head without using his claws. Here he is helping me feed them!
You can try introducing them slowly to each other and see how you go.
Ian.