Manchester City manager Pep Guardiola is anxious that the season could be over for Brazilian star Gabriel Jesus after suffering an injury while featuring for the club against Bournemouth.
He is now in Barcelona recovering from Thursday's operation.
But Guardiola's decision as to Jesus's replacement is complicated by the looming Champions League last 16 first leg tie with French club Monaco, which takes place at the Etihad on Tuesday. What's important now is a good recovery.
City could have a hectic last three months, with fixtures in the Premier League, Champions League and FA Cup, if they beat Huddersfield Town in the fifth round on Saturday.
Boss Pep Guardiola was pleased with Aguero's attitude when he was left out of the side and is confident City can rely on him for the rest of the season.
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The 30-year-old acknowledged that he is grateful for reaching 500 matches with the record European football champions Real Madrid. There is a high level of pressure on every player, but it will help them stay 100 percent concentrated in every game.
Initial estimates suggested Jesus will face between two and three months on the sidelines, meaning that a return to action before the end of the season is not out of the question.
"When Gabriel played in the last three games I didn't ask him to do what Sergio does, and I'm not going to ask Sergio to do what Jesus did".
Guardiola said: "It's not easy for the players who don't play, and have been out of the team for a long, long time in many cases, like Kelechi Iheanacho".
Aguero is still a world class option up front, but in Jesus Guardiola has a striker more suited to his needs.
"Sergio has to do what he has done all of his career, nothing more". Every player has his own quality.