The teenager, who was named on the bench for the first team's win at Newcastle on Saturday, was sorely missed in the U21s' goalless draw with Chelsea and 1-0 defeat away to the Magpies which have hampered the Reds' prospects of reaching the semi-finals of the competition.
Victory is surely required against Aston Villa on Monday night to keep the youngsters in the mix and the players will be eagerly anticipating another run-out at Old Trafford. Wilson, who had been sidelined with illness, is likely to return which could enable Andreas Pereira to revert to a deeper role.
"James is still growing and his body is still developing," explained Joyce to ManUtd.com. "His fitness levels have improved greatly this season from last year but he is still a developing boy.
"He's got a lot of potential and has that knack of scoring goals but he needs to keep working hard. I have got to say that he is a grounded kid but he must work harder now he's had a little bit of success. He needs a run of games and to be scoring every game between now and the end of the season. That has got to be his aim.
"It's been a little unfair on Andreas, playing him up front, but it's not doing any harm in a short period. He is more of a midfield no.8 or no.10 than an out-and-out forward but it didn't do Adnan Januzaj any harm last year and I think he has done well with the things we have asked him to do."
There is free entry for all supporters for the U21s game at Old Trafford on Monday night.