United sanctioned loan departures for midfield youth duo James Garner and Dylan Levitt in the summer, to Watford and Charlton respectively. Tahith Chong (Werder Bremen), Aliou Traore (OGC Nice) and Matej Kovar (Swindon) were among the other academy graduates to head out on loan.
United are considering recalling Wales international Levitt due to a lack of game-time at Charlton. Garner has fared a little better at Watford though has been left on the bench in recent matches.
Keane told the Manchester Evening News: “It's tough. I think the style of play, with these lads coming up through the ranks and then getting in the reserve team, they're used to that and it's a very technical game.
"And it's not men's football, so when you have that first exposure, it probably is a bit of a wake-up call to a lot of players, really. It's a different game.
"You step into a first-team environment; I remember my first experience when I was at QPR — I went to Wigan for an emergency loan for a few weeks first — but I went to QPR off the back of an injury and I hadn't really got myself back fit. I threw myself into it thinking it would be a really good opportunity, they were at the top of the Championship, and it was tough. For a young lad up front, you're playing against big centre-halves and you've got to put yourself about. And if you're not fully fit and ready for that, it makes it even more difficult.
“It's about them adapting to that and it's a results-based business. So if the lads aren't playing, maybe managers feel they've got to pick their team who they know are reliable and used to the level. They're not going to be waiting around for players if they're taking a bit of time to get used to it.
"The whole purpose of going out on loan is to get that game time and to keep developing as a young player. So if Levitt isn't getting the minutes at Charlton, you want to be somewhere where you'll be playing, to keep progressing."