Grealish has been preferred to Jeremy Doku and starts alongside Bernardo Silva, Phil Foden and Julian Alvarez behind Erling Haaland.
Manchester City are without Manuel Akanji. The defender is suspended following his red card against Brighton last weekend.
Kevin de Bruyne is the only other confirmed City absentee.
City will be looking to respond to wins for Tottenham and Arsenal, and Pep Guardiola said: "United have always had that feeling - it doesn't matter who the manager is - they are a tough, tough opponent.
"The qualities of the individuals they have, the stadium, the character they have, the momentum. They can score goals, we know the quality they have. Always that has been and always it will be."
Confirmed Man City XI: Ederson; Walker, Dias, Stones, Gvardiol; Rodri, Bernardo, Alvarez; Foden, Haaland, Grealish
Subs: Ortega, Phillips, Ake, Kovacic, Doku, Gomes, Nunes, Bobb, Lewis
Time and date: 3.30pm on Sunday, October 29, 2023
Venue: Old Trafford