Manchester United centre-back Vidic, 30, opted not to reverse his decision to come out of international retirement under new coach Sinisa Mihajlovic for the World Cup qualifiers.
Swansea ace Williams said: "Vidic is just world class. He's a great athlete, is so strong and a solid professional who does his job - he's a top defender. He's as good as anyone in the Premier League.
"It's a boost that he won't be playing as I'm sure Serbia would be better with him. It's good news for us."