The Manchester City striker is still suffering with a hamstring concern and remains a doubt for the Champions League clash, but there is more positive news on Fernandinho
The striker has been sidelined with a hamstring injury since January 29, with an initial prognosis of a month on the sidelines.
Pellegrini was more upbeat last week, insisting Aguero and Fernandinho were close to a full recovery, but the Argentine is still a major doubt to for the last-16 first-leg clash.
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"It's my opinion that for Aguero it is very difficult," Pellegrini told reporters.
"Fernandinho? Maybe if he worked with no problem and today he is 100 per cent fit - and if he does not have any fear about his injury - we will see if he can play.
"They have to be 100 per cent. If there is any risk of them being injured again, they won't play. We will talk to the doctor and see what happens."
Javi Garcia, meanwhile, returned from injury as City triumped over Chelsea to reach the FA Cup quarter-finals on Saturday, and Pellegrini is hoping the result can act as a springboard for both player and club.
"I think Javi played a superb game, in all senses - practical, technical," he said. "It’s not easy when you have just come back from injury after two or three weeks out.
"He is always an important option but at the moment I’m not thinking about what we’re doing on Tuesday. We will see how the players recover.
"I felt the team wanted revenge, not just against Chelsea, but also because of the Norwich game. I don’t think the team was fresh enough for those games, because they had played so many games in the previous two months."