Bale was in scintillating form against Scotland on Friday, scoring twice as Chris Coleman recorded his first victory as the Red Dragons' coach in dramatic circumstances.
"If we want to do anything in this group, it is so important that Gareth stays fit," said Williams.
"He was unbelievable the other night. He must be one of the best players in the world right night.
"We're pleased to have him. He's such a great player for us and there aren't many who can do what he did against Scotland."