When he first came into the team, he looked to have a really good footballing brain, he seemed to see the right pass better than our other players. He also had a great touch a a good range of passing.
He however lacked the legs and tenacity needed in midfield.
Recently the footballing brain seems to have weakened and he still needs to improve his work rate on the pitch.
This is all stuff that can be improved by attitude and hard work, the coaching staff should see through the day to day training whether they think Grealish has currently the right attitude, or is likely to change it, if he hasn't.
We as fans, can only really speculate what he's like in his head, and that's the important thing the management have to be able to judge right.