The 21-year-old went down after just nine minutes with what looked like a pulled muscle and hobbled off with a pained expression to be replaced by Antonio Valencia.
Eric Bailly, making his eleventh successive start, was also forced off soon after clashing with Fernando Llorente with 30 minutes remaining.
Mourinho wasn’t able to discuss the Ivorian’s knock after the game but noted that Shaw could be out for a lengthy period of time.
“I don’t know about the injuries,” he said.
“I think Luke Shaw‘s must be a big injury, because to leave the pitch after 10 minutes I am expecting a very big injury,”
“I prefer to speak about Juan Mata giving everything to be available. I am grateful for that.”
This could be a killer blow for Shaw’s Man United career: the next few weeks, coupled with the Under 21 European Championship in the summer, were meant to have been a platform from which to make a resurgence at Old Trafford – to show Mourinho that he had the required mettle to succeed at this level. A period on the sidelines – even for a two week period – will send the youngster back to square one.
But at least the youngster is somewhat replaceable, with Ashley Young, Daley Blind and Matteo Darmian capable of fulfilling the left back role. The same cannot be said for Bailly: he was United’s last available recognised defender but following almost eleven straight games – 960 uninterrupted minutes – the Ivorian has finally reached breaking point.
Mourinho may well have to ask around for a spare pair of boots ahead of Thursday’s trip to Spain.