But the England international insisted there was 'no chance' and hinted at three nights of partying.
Grealish was an unused substitute as Pep Guardiola's side came from 2-0 down with three goals in five minutes against his former side Aston Villa.
It sparked wild celebrations at the Etihad, which continued in the dressing room as Grealish posted a photo of himself getting on the beers on Instagram.
The caption read 'Ooffffft the first of many' - and Keane, speaking to Grealish on the pitch after the title win, urged Grealish to steer clear of the stronger stuff.
Keane said: "Keep off the top shelf, stick with beer."
And Grealish responded with a laigh: "Not for the next three nights. No chance."
Fellow Sky Sports pundits Micah Richards confirmed he was going out with Grealish and the City boys, with Keane joking that he'd be driving after the pair extended an invite.
Keane, who won seven Premier League titles with United, was forced to endure City's title celebrations and admitted it was torture.
"Absolutely, it's great to be here. Fantastic," said Keane as ex-City star Richards danced in front of him. "Torture!"
However, the Republic of Ireland legend had to give City credit for turning it around against Villa.
Keane said: "The bottom line is, the challenge City faced today was in front of them, Aston Villa.
"You know you've got to score three goals to win the title. That's huge pressure. You've got to get the ball running.
"Credit to City. Them and Liverpool are the hardest working teams."