The City boss had expected to be without the Argentine, who suffered a muscle injury against Chelsea three weeks ago, and officially ruled him out at Friday’s pre-match press conference.
There was better news regarding Zinchenko, however, who is fit enough to be considered for selection after recovering from a knee injury.
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“He’s been training for the last few days,” said Guardiola.
“He trained with all the squad. He’s ready, but in his physical condition I don’t know how many minutes he can play.
“Sergio is not available.”
Both teams come into the game on the back of morale boosting midweek victories.
City beat Burnley 4-1 on Tuesday evening, while United edged Tottenham Hotspur 2-1 on Wednesday for the second win in their last five league games.
It leaves them 11 points behind City in sixth place, but the Reds boast the superior record in this contest and while Guardiola admitted Saturday's opponents have plenty to admire, he refused to accept history will have any bearing on the outcome of the latest clash.
"It’s Manchester United,” he added. "All the respect for what they have done for English, European and world football. They are a good team.
“I judge specific players, specific qualities. They're incredibly fast up-front, good set pieces with [Harry] Maguire, [and have] physicality and aggression. I had a good impression when I saw them.
"Normally we talk a little about what happened in the past, but everything is changing. I couldn't care less [about past results]. Tomorrow is a 5.30pm start and the players decide who will win.
"History is huge and the quality of players they have has always been there and you have to try to beat them and we have spoken to the players on how they could beat them."
City will be looking to inflict a third successive derby defeat on United, who have been denied the services of the injured Paul Pogba.
Manager Ole Gunnar Solskjaer has acknowledged the defending Premier League champions are a difficult proposition, but feels victory in a game of such magnitude could prove to be a catalyst for an upturn in fortunes.
"We're going away against arguably the best team in England," the United manager said. "It will be a difficult game but we need consistency.
“Before everyone was doom and gloom but it's a chance to turn that doubt into belief and if we can manage to get another performance, the confidence, the way we played against Tottenham, then we can come out of it with a result.”