The 21-year-old has endured a difficult couple of years since heading to Old Trafford in 2014.
He was restricted to just 20 appearances in all competitions in his first 12 months with the Red Devils.
And last season was cut short by a horrific double leg break suffered against PSV Eindhoven in the Champions League.
This year he was expected to realise the potential which saw Louis Van Gaal splash out more than £25m to secure his services from Southampton.
However, he has failed to show his best form and he was torn into by Mourinho for being at fault when United conceded the second goal in a 3-1 defeat to Watford in September.
England international Shaw was expected to feature against Swansea on Sunday.
But, speaking after the 3-1 victory at the Liberty Stadium, the United ace's manager said he had opted out of the Premier League clash.
"To compete you have to go to the limit," Mourinho said. "It is cultural for some – and that is not my culture. More than me, it is Manchester United.
"We have players with 'problems.'
"At every sport - and I know because I have friends in other sports and they play at the highest level in their sport - and how many times they play when they are not 100 per cent."
According to The Sun, Mourinho’s decision to have another go at Shaw has left him baffled.
The left-back is said to still be seeking to return to 100 per cent fitness.
And Mourinho’s questioning of his attitude, particularly in light of his recent return from a serious injury, has apparently left Shaw taken aback.