I'm starting to question whether alot of this speculation has to do with his agent creating a buzz to get Vidal a new contract Rooney style. According to some research, his contract expires in 2017 which by then he'd be 30 and not the best age to negotiate a huge deal. At his age and with his standing as one of the best right now, this is the best and maybe last chance for him to land one last huge multi year deal at a top European club. All the media speculation is coming from Chile and Italy, places where Vidal's team will have the most ties. The agent feeds the press stories about Real Madrid and Manchester United, whether true or not (I highly doubt Real Madrid's interest), but it makes other clubs take notice and causes a bidding war where the money offered to player and agent increase.
I can guarantee that if he comes back on Monday and pledges his future to Juventus, a new deal for Vidal will be announced shortly thereafter.