The 21-year-old defender is reportedly in talks with Spurs over a move ahead of the new season.
Having committed his own future to the Swans last week, Williams now hopes that Davies will follow suit.
"It is down to Ben what he wants to do," he told the South Wales Evening Post. "I have not had the chance to chat with him, but obviously I am close to Ben, we have played a lot together and get on well.
"I have seen him grow. We know he is a mature, sensible lad and he will do what is best for him. I will try to advise him, but I would not tell him to stay because I want him to stay."
Swansea begin the new Premier League campaign with a trip to Manchester United on August 16.