With Darmian set to leave the club, United could be without a right-back when they take on Leicester City in their first game of the new Premier League season, as Antonio Valencia and newcomer Diogo Dalot are both injured.
Manchester United will have to pay an inflated transfer fee to sign Inter Milan winger Ivan Perisic this summer, according to a report in England.
That's after Mourinho said before United's opening pre-season tour match in the U.S. against Club America that Dalot would be unavailable for the start of the season due to injury and that it was expected the defender would be "ready for September".
The former Chelsea boss had also predicted a tough start to the new season, even though the club will be favourites to beat Leicester and Brighton in their opening two fixtures.
Manchester United have struggled to impress in pre-season with a patchy squad that has been depleted through injuries and key players resting after the World Cup in Russian Federation.
Already deprived of more than half of his first-choice starting XI because of World Cup commitments, injuries have now decimated his squad and Mourinho is anxious as he moves towards the start of the serious business of a new domestic campaign.
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Obviously it could have got awkward, but (Froome) you've been a great champion and I'll always have respect for you. Oh, and my wife. "Now he's being repaid for all the years of hard work and sacrifice he made for the team".
Mourinho had been banking on starting the Premier League season with a back four of Valencia, Shaw, Bailly and Smalling, but all are now injured or carrying knocks, throwing his preparations into disarray ahead of the home game against Leicester on August 10.
"We basically have the same players".
And I wait to see if it's possible to have one of these players.
"The players we have bought - one is a goalkeeper cover, one is a 19-year-old kid, so in fact we have one new player, which is Fred".
Darmian only made eight appearances in the Premier League last season - including just five starts - as well as 17 across all competitions.
Mourinho has praised their commitment and dedication, revealing Bailly had asked to play on Sunday when Chris Smalling started limping in the warm up because he wanted to protect United's young players. What I don't agree with is that the Premier League starts now.