Manchester United manager Jose Mourinho has questioned Luke Shaw's commitment to the Old Trafford club.
The 21-year-old defender has only played 15 times for the Reds this season and has not figured since last month's 1-1 draw against Bournemouth.
And Mourinho claims he compares unfavourably to fellow defenders Ashley Young, Matteo Darmian and Daley Blind.
"I cannot compare the way he trains and commits, the focus, the ambition. He is a long way behind," he said.
Mourinho was asked by reporters whether he expected more from an England international.
"Joe Hart is an English international and is playing on loan in Italy," he responded.
In November, he was criticised by Mourinho for missing the Premier League win over Swansea after he said he was not able to play.
He was not part of the squad for Saturday's 0-0 draw against West Brom, despite United's lengthy injury list with Juan Mata (groin surgery) the latest addition joining defenders Chris Smalling and Phil Jones and midfielder Paul Pogba.
Mourinho, who was criticised by Match of the Day 2 pundit Chris Sutton for his side's lack of attacking threat, is unsure whether the Frenchman will return for Tuesday's Premier League visit of Everton.
"Pogba I cannot say he is ready for Tuesday because I don't know," he said. "I think Mata, Jones and Smalling for a long time, but I don't think Pogba is such a long-term injury as the others."
Former Manchester United defender Phil Neville on BBC Radio 5 live
"Jose has probably tried lots of things. This might be the final throw of the dice for him to publicly say this is why Luke Shaw is not playing because he is that far behind the levels you need to play football for Manchester United.
"He (Shaw) needs to take a long hard look at himself. He should be England's number one left-back and he should be United's. At the moment, he is fourth or fifth in line and that is really disappointing.
"Sometimes you need a jolt. This might just be what he needs."