It is a boost for quadruple-chasing City as they look to extend their 14-point advantage over second-placed United in the fixture at the Etihad Stadium.
City boss Guardiola said: "Good news for us, Nathan is back. He made part of the training session and felt really good.
"Everyone is fully fit and that is important for the next few weeks ahead of the international break, and hopefully the people will come back well after that."
The fixture is important in the context of the title race and Guardiola expects it to be a difficult encounter.
Ake's return means Guardiola's key decisions are likely to come in defence and attack: the likes of John Stones, Aymeric Laporte and Ruben Dias will all want to start at centre-back, with Kyle Walker, Joao Cancelo and Oleksandr Zinchenko pushing for wing-back roles.
With Kevin De Bruyne and Ilkay Gundogan likely to take two of the three midfield roles, Rodri and Fernandinho are vying for the holding role.
In attack, Raheem Sterling is most likely to lead the front line ahead of Sergio Aguero and Gabriel Jesus, with Riyad Mahrez in form and set to start on the right with Phil Foden, Ferran Torres and Bernardo Silva all in with a shout on the other flank.
Man City predicted lineup (4-3-3): Ederson; Walker, Dias, Stones, Cancelo; De Bruyne, Fernandinho, Gundogan; Mahrez, Sterling, Foden
Injury list: None
Doubts: Ake (match fitness)
Additional reporting by PA.