Sanchez accepted a 16 month suspended jail sentence in February for tax fraud in Spain and under American law, no one found guilty of fraud can be granted a visa to enter the country.
It's since been confimed that his absence from the tour is due to legal issues whilst trying to obtain a visa. Speaking to reporters before United's pre-season gets underway, Mourinho said, "I've no idea".
Topflight Premier League side Manchester United commenced their pre-season training in America without a complete squad as Portuguese boss Jose Mourinho put his players to work. We think he can start training back in England, not ready for start of the season'.
"It's not good for anyone but there is no one to blame".
"There is no [Romelu] Lukaku, [Marcus] Rashford or [Jesse] Lingard". It's good for him to play but then he will go on loan.
"Now I look at it as a full preseason for me, and right now things are going really well".
"But there is no one to blame, the club is making the effort, I have to respect the USA authorities in their process of visa selection".
That's the verdict of former Arsenal ace Stewart Robson, who says the winger's impressive World Cup will have reignited United's interest.
"I think he had a good enough World Cup for Manchester United to be interested again".
The left-back has struggled to establish himself since Mourinho arrived in 2016 and started just eight Premier League games last season.
The Old Trafford side also play a friendly against German champions Bayern Munich on August 5, five days before they kick off their league campaign against Leicester City.