Pep Guardiola's squad flew to Lisbon on Monday to prepare for Saturday's quarterfinal showdown with Lyon, but Aguero remained in Barcelona to continue rehabilitation on a knee injury he suffered during June's 5-0 trouncing of Burnley.
Aguero has reportedly confided with friends that it's unlikely that he'll feature in the last-eight tournament in Portugal while he recovers from the setback, which required surgery. He may join City at the competition but it's unlikely that he will be fit to play.
In his absence, Guardiola started young playmaker Phil Foden in a false-nine role in last Friday's 2-1 win over Real Madrid. Gabriel Jesus, often Aguero's deputy at City, played on the left of a narrow, three-pronged strikeforce with Raheem Sterling operating from the right. City signed off the two-legged affair with a 4-2 aggregate victory.