Joyce has overseen the development of players such as Marcus Rashford and Jesse Lingard and also worked with Paul Pogba while he was at the club the first time around.
His outburst came on MUTV after United’s U23s lost 2-0 against Southampton at St Mary’s on Monday.
“It’s not the first time I’ve actually said to this group straight after the game ‘you’re actually embarrassed — the way we’ve played,’” he said. “It’s probably the third time in the preseason games.
“It’s not an automatic thing at this place that players just go on and be successful, as they have been in the last few years, where if they’re not good enough to play for Manchester United they drift into leagues and have successful careers.
“This group are almost deluded really, as to where they’re at. And there is certainly a lot of hard work to be put in during the coming season to keep our head above water, really.
“There’s no shame in not quite being good enough to play for Manchester United but you can’t be deluded and think you’re further along than you are as well.
“We were second best by a long way.”
Joyce added he is frustrated by what he is seeing among the current crop of players and suggested they look at previous youth players at the club to see how much commitment is required to progress on to a successful professional career.
“You want your team to have the personality of yourself, so that’s why it’s frustrating for myself really. I think I’ve got a little bit more ambition than some of them have, for them to have successful careers.
“There are one or two who have been in and around the group, while not necessarily in the team, for a while now, and they’ve got to look at the players that have gone in the past and what they’ve had and what they’ve given and what they’ve done, and how much desire and drive they have to play for the club and try to play for the first team.”