"It is difficult for him to be on the bench," Mourinho was quoted as saying by British media on Monday. "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."
When asked if more should be expected of an England international, Mourinho added: "(Manchester City's) Joe Hart is an English international and is playing on loan in Italy."
Shaw, who joined United for 27 million pounds ($33.87 million) in 2014 from Southampton, was left out of the squad for the 0-0 draw at home to West Bromwich Albion on Saturday.
News that makes sense
Your trusted source for staying up-to-date with the world around you. Get free daily news updates and analysis, straight to your inbox.
Turning to his injury-hit squad, Mourinho said he was not sure if France midfielder Paul Pogba would be fit for Tuesday's Premier League game at home to Everton.
"Pogba I cannot say he is ready for Tuesday because I don't know," he said. "I think (Juan) Mata, (Phil) Jones and (Chris) Smalling (will be out) for a long time, but I don't think Pogba is such a long-term injury as the others."
Smalling, who has been wearing a leg brace, and Jones (toe)were injured on international duty with England, while Spaniard Mata has had surgery on a groin problem.
However, Mourinho does have striker Zlatan Ibrahimovic and midfielder Ander Herrera available again after suspension.
($1 = 0.7972 pounds)
(Writing by Ken Ferris; Editing by Greg Stutchbury)
