Left-back Shaw has struggled to feature under Mourinho despite injury absences in defence and last played in the 1-1 draw against Bournemouth last month.
Mourinho has indicated the defender won't be involved in the Premier League clash against Everton on Tuesday, per The Independent's Tim Rich: "It is difficult for him to be on the bench. I cannot compare him with Ashley Young, with Matteo Darmian, with Daley Blind. I cannot compare the way he trains, the way he commits, the focus, the ambition. I cannot compare. He is a long way behind."
Shaw made a long-awaited return from a fractured leg last year and was expected to pick up his United career where he left off, although Mourinho's questioning of his character suggests there are deeper issues in play.
Rich indicated Mourinho's comments "signalled that Luke Shaw’s Manchester United career is over," and one might find it hard to disagree if the left-back can no longer even guarantee his place on the Red Devils bench.
Shaw was brought to Old Trafford from Southampton by Mourinho's predecessor, Louis van Gaal, and was one of the Dutchman's first signings during the 2014 summer transfer window, arriving for a fee of £30 million.
It was around that time then-Chelsea manager Mourinho missed out on the left-back's signature and instead recruited Atletico Madrid's Filipe Luis, suggesting Shaw's wage demands were the reason why, per Rich's report:
If we pay a 19-year-old boy what we are being asked for to sign Luke Shaw, we are dead. We would have killed our stability with financial fair play and killed the stability in the dressing room. We would have had players knocking on our door, saying: ‘How come I play 200 games for Chelsea, win this and that, and a 19-year-old comes here and gets more money?’
Mourinho's latest comments came after Saturday's disappointing 0-0 stalemate at home to West Bromwich Albion, giving at least some indication as to why the manager's outburst has even come about.
The Red Devils chief will undoubtedly be upset with the fact his side missed out on more points at the start of a packed April schedule, although football writer Lars Sivertsen described it as nothing more than diversion tactics:
If that is indeed the case, Shaw will understandably feel some contempt at being the target of Mourinho's ire, especially when converted midfielder Ashley Young and right-back Matteo Darmian are among his main competitors at left-back.
United would struggle to regain the £30 million investment they made to sign Shaw three years ago in the event they chose to sell this summer, although Mourinho appears willing to settle for a loss at this stage.