A muscular problem has kept Ake out for two months, with his last appearance coming in the Boxing Day win over Newcastle United, but the Dutch defender has responded well after returning to full training earlier this week.
“It’s good news for us,” said Guardiola at his pre-match press conference.
“Nathan is back. He made the training sessions and felt really good.
“Everyone is fit. It is important for us and hopefully at the international break everyone comes back really well.”
Whilst City will have a full complement of players, the same cannot be said of Manchester United, who could be without up to six members of their squad.
Juan Mata and Phil Jones are both unavailable, whilst Ole Gunnar Solskjaer has confirmed David De Gea will miss the game following the birth of his first child.
Anthony Martial, Donny van de Beek and Paul Pogba are all doubts after missing the midweek draw with Crystal Palace.
Victory on Sunday would see City open up a 17 point lead over United at the top of the Premier League table ahead of the final 10 games of the campaign.
Guardiola’s side are on a 21 match winning streak, but whilst United are coming off the back of three consecutive 0-0 draws, they have not lost away from home this season.
The Reds have won three of our previous six meetings and the City boss acknowledged his in form team are in for a tough afternoon, but says his players understand the significance of the game and its ramifications.
“It’s important this game,” he added.
“It is, like the previous one, the previous one and the next one.
“I know how difficult United are. I have the feeling they are a better team every season. They haven't lost away for more than one year.
“They always get good results here at Etihad Stadium, but we know the opportunity we have to extend our advantage.
“The Premier League is 38 games, this is one of them. Obviously, they are now real contenders, second in the table.
“Everyone knows how important it is. We will try and win the game.”
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