Grealish is incredibly important. He always wants the ball and is available for a pass and then when he gets the ball he doesn't lose it and wins freekicks etc.
Additionally from the BBC:
Jack Grealish created three chances for Man City tonight, taking his Champions League tally for the season to 35. It's the most of any player this term, and the most on record (since 2003-04) by an English player in a single campaign.