The Argentine striker has been struggling with a knee injury and hasn’t played since the 1-0 win over Chelsea at the beginning of March.
Pep Guardiola says he is making good progress in his recovery but admits the first leg of our Champions League quarter-final tie at Anfield has come too soon.
"Sergio is back in Manchester,” Guardiola said. “He did not come. He was injured in the last two weeks.
"He is much, much better but the doctors spoke to him today and he said he still has a little bit of a problem and isn’t comfortable.”
Asked if Aguero could be fit for the Manchester derby on Saturday, Guardiola said: “We will see."
Meanwhile, the City boss revealed Fabian Delph is available for selection again.
Delph’s last match was the FA Cup defeat to Wigan in February, a game that saw him receive a red card.
After serving a three-game suspension, he then suffered a muscle problem but is now fit and ready to challenge for a position at left-back on Wednesday.
"Fabian Delph is back, Danilo can play there,” Guardiola said.
“I have an idea [about who will play] but you understand I can’t tell you!”