Guardiola commented on Grealish being spotted on a boozy night out earlier this week.
Ahead of today's trip to Nottingham Forest, Guardiola said: "They know what they have to do.
"They have private lives to do whatever they want. I'm not going to control what they do in their private life.
"I judge what I see on the pitch, the training sessions and the performances in the game. That's where I judge the players.
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"I want Jack at his best, of course, but he had setbacks and didn't play but that was sometimes for the injuries, he could not get the rhythm that you need for being ready every three days."
Asked if Grealish will stay next season, the manager also said: "He is a player for Man City. What will happen? I don't know what is going to happen.
"What happens in terms of Jack, in terms of everyone, will be treated at the end of the season. But now we are playing for many important things for the club."