The forward was not able to travel to the United States with his team-mates after his visa application was blocked.
Sanchez subsequently missed the first game of United's pre-season tour, a 1-1 draw against Mexican giant America.
But United posted a video of Sanchez signing autographs at a training session on Sunday (AEST) after safely arriving in LA.
With attacking team-mates Romelu Lukaku and Marcus Rashford on holiday after the FIFA World Cup, Sanchez is in line to play in United's next friendly.
Jose Mourinho's men face San Jose Earthquakes on Monday (AEST) ahead of International Champions Cup matches against AC Milan, Liverpool and Real Madrid, rounding off pre-season against Bayern Munich.
United will then kick off the 2018-2019 Premier League season with a home game against Leicester City on 11 August (AEST).