The 19-year-old, who joined United on a five-year contract last month, sustained the injury while playing for former club FC Porto in the closing stages of last season.
Among the United players to have travelled to Los Angeles are midfielders Juan Mata and Ander Herrera plus defender Antonio Valencia.
Mourinho said the 25-year-old was "absolutely brilliant" in Les Bleus' final three matches in Russian Federation. It's time for me to show him I can be in the team'.
"I think that's the point, about his performance level and his contribution to a winning team".
'The year I broke my leg I felt strong - it was unfortunate. "I sent a nice message before the World Cup and during it I did not disturb anyone".
"It's a young [France] team, apart from [Olivier] Giroud, [Hugo] Lloris and a few others they are all young and have more years to play together".
Rescued boys from Thai cave make public appearance
They also described the meals they'd eaten while at the hospital for the past week - pork and rice, bread with chocolate spread. The boys were taught how to meditate to conserve energy , and many avoided thinking about food in order to stave off hunger.
The Portuguese was also vague on whether are new signings are close to arriving, although that is probably sensible given the fact there is going to be made dash in recruitment in the remaining three weeks of the window.
The Red Devils won both the Europa League and League Cup in Mourinho's first campaign in charge but they ended up without any silverware last term. "That complicates things. I would lie if I said I am not anxious about it, but it is what it is".
De Gea, Matic and Fred are due to join the squad next week before the third tour game against Milan in Los Angeles.
According to the BBC, Sanchez is trying to get into the United States under a visa-waiver scheme.
"If Alexis is not working with us for 15 to 20 days, it will be very bad", Mourinho said. "Just enjoy the games and I know he will become better". I have to respect the US authorities in their process of selection of visas. "He is recovering really well", Mourinho added.