Chilean forward Alexis Sanchez also failed to make the trip after a visa issue, leaving Mourinho anxious about starting the league with fewer senior players.
"Hopefully he [Sanchez] join us later", Mourinho said.
"The club is making the effort, I have to respect the USA authorities in their process of visas but hopefully he joins us later because could be important to work with [Anthony] Martial and [Juan] Mata, which is the players we have in attack for start of the season".
The design of Manchester United's new kit has split opinion among fans, but there has been universal scorn over the price tag for the 2018-19 home strip.
Having posted the pictures of the former Barcelona star training at the Carrington base last week with more images emerged of him with friends in Cheshire on Sunday. "I look back over the last few years and I've not had a massive run in the team", Shaw told reporters.
"The year I broke my leg was the best year in my career at United".
"It is really bad, it is really sad", Mourinho said.
'I don't know about Sanchez.
"I hope he understands why he was very good".
Blind moved to Old Trafford in 2014 for £14m and will return to Holland for a similar fee.
And according to The Independent, Juve have named their price for Sandro.
The club said the latest jersey marks 140 years since the club was founded, with a train track graphic referencing United's original name: Newton Heath Cricket and Football Club.
"I wanted Ivan Perisic".
"To win the World Cup can only be a positive thing", added Mourinho.
Presumably, both Sanchez and Martial, in particular, will get the early opportunity to impress due to the longevity of both Romelu Lukaku and Marcus Rashford's World Cup campaign's that saw both players reach the third and fourth place play-off with Belgium and England respectively.
But he missed out on a deal with United unwilling to meet the asking price Inter Milan had slapped on the Croatia worldwide.
Mourinho also had words of encouragement for Paul Pogba, who won the World Cup with France, scoring in the 4-2 victory over Croatia in the final.
Robson, who now works as a pundit in the United States of America, is backing the 29-year-old to finally seal his switch to Old Trafford this summer.
NAIJ.com previously reported that Alexis Sanchez may be sentenced to jail for evading taxes worth over €980,000 between 2012 and 2013 when he was a Barcelona player.
Adidas were applauded for the stellar work they did on nearly all of the national team kits for the World Cup in Russian Federation this summer, and they deserved it.