Manchester United is banned Alejandro Garnaacho, Antony, Jadon Sancho and Tyrell Malacia.
The banished quartet is kept away from the first team when they return from the US next week.
The 'Bupploeg' of four men may continue to use the facilities on the club's training field.
But they get a “different schedule” from their teammates to keep them separate.
Sources said the club discussed that they were driven to become a member of the U21s, but the exclusion for fear of a legal protest.
One said: “They will train together as a group, but according to a different schedule than the first team.
“The first team will train in the morning. They will train in the afternoon.”
The humiliating movement comes after they had been left at home for the pre-season tour by the US.
They were also told by Hardline Red Devils -Baas Ruben Amorim to use the time to find a new club.
Another source with knowledge of the situation said: “Their days at United are numbered.
“As such, it would be inappropriate to stay around the first team.
“When the team will return to Carrington next week to continue their training for the season, they will be kept away from their former teammates.
“Ruben is determined to promote a new culture in Old Trafford.
“The players are all on board and he does not want distractions if they close at the start of the new season.
“He wants to create an intimate team binding.”
Amorim is under an enormous amount of pressure to deliver after a disastrous season, they saw 15th ending – their worst season since they were relegated in the 1973-74 campaign.
Their misery was exacerbated by the 1-0 defeat in the Europa League final to Tottenham.
Luke Shaw van United said he supported Amorim's hard posture to clean up things after burning the dressing room “toxic”.
Shaw, 30, admitted: “It is not difficult to see from the outside what it has been like.
“I have often been here in recent years, it was extremely negative.
“It can be quite toxic, the environment, it is not healthy at all.”
The Red Devils lost their way under Interim boss Ralf Rangnick and then Erik ten Hag, before the arrival of Amorim in November last year.
Transfer News Live – Stay informed of the last from a busy summer window
Shaw said none of the players had been good enough.
And in a veiled wipe with the four outcasts, he added: “But there are no left behind in this group.
“That is due to the mentality of Ruben, his requirements. Everyone has to put the team first.
“He made that very clear and he chooses players who he thinks will be best for the team.”
Amorim's reconstruction work at Old Trafford has already seen the arrival of £ 62.5 million signing of Matheus Cunha van Wolves.
Forward Bryan Mbeumo also came to Brentford in a deal that could be worth £ 71 million.
But United is still not done in the transfer market and are heavily coupled with a movement for £ 70 million with Ace Benjamin Sesko, 22, from RB Leipzig.
Manchester United opened conversations with their priority No9 after Aston Villa insisted that Ollie Watkins was not for sale.
United Director of Recruitment Christopher Vivell and negotiator Matt Hargreaves flew to Germany in an attempt to close a deal for 6ft 5 in Slovenian Sesko.
The club wants to generate more funds by selling the 'Bomb Squad'.
Marcus Rashford joined Barcelona on a season loan after he had gotten out of favor.
And Argentinian winger Garnacho, 20, is all the subject of a relocation of £ 45 million to Napoli.
United wants £ 70 million for Garnacho, but still has to receive an offer.
Borussia Dortmund will offer Sancho the chance of a third spell at the club.
Juventus was the most likely destination, while the Serie A champions Napoli also performed their interest.
But Dortmund coach Niko Kovac is now insisting on a dive of £ 17 million for a player who has made his name with them.
United starts the new Premier League season with a Nightmare Home Tie against Arsenal on August 17.
And Amorim is determined that the players must be ready – on it: “We have to use every minute in every week of the preseason … we have to arrive in shape.
“It's the only way to take action to get better next season.
“They know that everyone knows that the following year will be huge for everyone.”
The Red Devils compete against Everton on Sunday in their last American summer break match before they fly home.