Castles said on the Transfer Window podcast: "This summer United have chose to go for Alex Sandro". They have put a deal in place with the player, the player wants to (join) and Juventus are holding out for up to 60million euros (£53m).
After arriving at Turin in a €26m move from Porto, Sandro has been fundamental to Juventus' success in recent years.
Shaw is now looking to prove the manager wrong, and he needs to impress this year if he has any chance of receiving a new deal from the club. And why does Mourinho think the 17-year-old is ready?
However, when asked about where he would play in the upcoming season, he revealed that his decision will be known soon and his main intention is to play at the top level - the Premier League.
In addition, Juventus are also looking to bolster their squad this summer, after nearly being toppled by Napoli last season.
It would be disappointing for us to lose out on the star should he really be sold this season.
Meanwhile, the Red Devils' pursuit of Alex Sandro has been somewhat of an absurdity.
The Man United man has given himself a head-start on team-mates after returning to training early and replied to a tweet about his fitness saying "I'm not finished yet".
However, at the age of 32, the English global is nearing the end of his playing career.
Juventus believe Manchester United have been demanding too much money for player who is out of contract at the end of next season, but the Premier League giants have been refusing to stand down.