It has been claimed that the bus that took the squad to Manchester Airport for their flight to Ukraine left the club's training base in Carrington without the England youngsters on board.
Instead, they remained inside the facility, despite a security firm being employed to ensure that the entire playing staff was present.
"The security firm United employ, CES, are supposed to check the numbers. They have a bloke with a clipboard who stands at the front and ticks all the players and staff off a list," a source told the Manchester Evening News.
"He said that they were all on board and they set off down the lane and out past the barrier. Danny Welbeck and Chris Smalling then came running out of the main building.
"Apparently Chris had gone pale and asked where the coach was. When he was told it had gone he said 'we were supposed to be on it'. They managed to get a message to the coach and it came back and picked them up. The other players were laughing their heads off. You couldn't make it up."
When asked about the alleged incident by the MEN, United opted not to comment.