Rushworth has impressed for the Swans this season.
Williams said: "Yes (he can play for England), he's that good.
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But it's not just about how good you are as a player or goalkeeper. It's also about the personality, and he's top."
He added: I think he will be the first to say that he has worked with the top goalkeeping coach and it's been a good experience for him.
"He has played for a really top club and had a lot of minutes in a really good league so it has been really beneficial all round for everyone.
"I think it's likely he'll be playing in the big league or in the shake-up for that.
"That's what I anticipate."