As revealed in an article from Daily Express and as you can see in his last tweet, things are clear now:

Arturo Vidal “At this point I do not go away, I stay at Juventus”

The Red Devils had been hoping to land the Chile international before the transfer window closes on Monday night, with a bid of £34million plus Javier Hernandez in the works.
Vidal was believed to have agreed personal terms with Louis Van Gaal’s side on a five-year deal worth £182,000-per-week, but as revealed earlier by Express Sport, Juventus are reluctant to part ways with their star man.

United chiefs had been confident that the former Leverkusen man would make the switch following the capture of Real Madrid’s Angel Di Maria, but according to reports in Italy, Vidal has told friends that he won’t be leaving Turin this summer.

The 27-year-old is recovering from a knee injury sustained before the World Cup, and is quoted as saying: “At this point I do not go away, I stay at Juventus.”
The revelation will come as a shock to Van Gaal, as it implies that had a move been negotiated earlier in the window, Vidal could very well have ended up at United this summer.