The Chilean was not part of the 24-man squad that departed for Los Angeles on Sunday evening, instead staying behind in Manchester. He was pictured with friends in Wilmslow, Cheshire, earlier on Sunday.
But it has now been confirmed that Sanchez has been given time to resolve a personal administrative issue, and the club are hopeful that he will be free to join them within the next 24 to 48 hours.
Sanchez faced going to trial in Spain over unpaid taxes of around €1 million relating to image rights deals between 2012 and 2013 when he was playing for Barcelona.
The United boss will be looking for evidence over the coming games that he can "trust" Shaw, with the team set to face Mexican side Club America, San Jose Earthquakes, AC Milan, Liverpool and Real Madrid stateside, before a clash with Bayern Munich in Germany.
Chelsea boss Maurizio Sarri is keen to add to his squad this summer
Sanchez agreed to repay the money in full and accepted a 16-month prison sentence which means he did not have to go to jail because the punishment was less than two years.
There is a waiver scheme and it is understood Sanchez is working with his lawyers in an effort to be granted access to the United States.
Manny Pacquiao's career on the line against Lucas Matthysse
And Matthysse's trainer Joel Diaz hit back at accusations that his fighter was only in Asia to pick up a big pay day. "It will. He said it has been his dream since young to fight Pacquiao, an 11-time world champion across eight divisions.
Two Die In France After World Cup Celebrations Turn To Chaos
The Champs-Elysees Clemenceau has become the Deschamps-Elysees Clemenceau to honour national team coach Didier Deschamps . Meanhwhile in Saint-Felix, another fan in his thirties died as his auto crashed into a tree as he celebrated the win.
Trump's "low expectations" for Putin summit
Mr Trump said during the meeting that the United States and Russian Federation would have an extraordinary relationship. Russian officials say Putin is expected to reiterate denials of meddling in the 2016 U.S. presidential campaign.
Croatian leader says Trump, Putin key to peace
The First Woman President of Croatia, traveled with fans in economy class, and support their team with the crowds in the stadium. Reportedly, the first lady of Croatia didn't even miss one match of her team.