We don't know what happens on a daily basis. One thing is preseason which is a bit of an easier experience for young players, but who's not to say that everyday in training he's not getting knocked off the ball easily by players like Lingard and whilst demonstrating clear signs of quality he's just a bit short in the physicality at the moment?
If every days he's training with the first team and making players like Lingard and Pereira look awful, you can guarantee he'd be in the matchday squad.
However, as much as you don't want to believe it, it's clearly not the case. He must be struggling when compared to those players or he would quite simply be ahead of them.