The Red Devils now have a good relationship with the lower division club for such matters.
They had Finley McAllister and Malachi Sharpe spend time with the South Yorkshire team.
Doncaster manager Grant McCann spoke to the Doncaster Free Press about this arrangement, stating: "We've had a couple of boys in this week from Man United. They've been training with us and that's been really good, just to have a look at them. We also sent two to Man United.
"It's about forming a relationship with them which is great and there's other clubs that want to do that as well and that speaks volumes about how we're playing and performing.
"It's really good to have a chance to look at things like this. They're two of Man United's better U21 players and they both played in the game (behind-closed-doors) and were both excellent.
"One's a wide player (Sharpe) and the other is a midfielder (McAllister).Travis (Binnion) has been brilliant with us and the fact we've managed to get Kasper and Sam in there is great, to show them what a Premier League club looks like but also to see they work and train and deliver sessions.
"It's been a worthwhile week and having that link with one of the biggest clubs in the world is huge. If you're a young player at Man United then you've got everything there. They have the best training ground, the best pitches, best food. Everything is just laid on for you.
"I remember when they came to us (EFL Trophy group game) wearing brand new Hugo Boss suits. We're in our tracksuits, so it's just a different world. But coming here gives them an insight into what it means to win three points as opposed to U21 football where it doesn't really matter. It's a huge thing."
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