The 21-year-old has previously made headlines for drunken behaviour and inhaling nitrous oxide - known as laughing gas - and he was in the gossip pages again this week.
Grealish is alleged to have visited a hotel party in which nitrous oxide balloons were used, which has prompted Xia to contact the midfielder on social media.
The Chinese businessman wrote: "As I said before, focus every minute on and off pitch, choose the right type of people to be with. Don't let people who trust you down!"
Xia insisted that he was looking out for Grealish like an "elder brother" rather than criticising him.