"With the way the fixture list has been, we've not had enough games," conceded Joyce.
"Obviously there has been the Under-19 competition (the UEFA Youth League) too so we don't seem to get the same team out for two games on the trot."
The Under-21s' next outing is another home game at the AJ Bell Stadium, against Manchester City next Monday evening. United are in seventh spot in the table, above the Blues on goal difference, and three points behind sixth-placed Southampton with two games in hand on the Saints.
The top four in the 22-team division qualify for the end-of-season semi-finals with Fulham, Liverpool, Chelsea and Sunderland currently filling those positions.