The Argentine striker started for just the second time in a Premier League fixture since late January when scoring early in City's eventual 3-1 victory over West Bromwich Albion at the Etihad Stadium before he was subbed off in the 64th minute.
Aguero has made only 20 league appearances this term, for an incredible 16 goals, which prompted Pellegrini to speak highly of his influence on the City side and the fact that his absence sees the 2012 champions sitting six points league leaders Liverpool.
"Kun is a top player, he makes the difference - that is why playing this year without Kun for 12 or 14 games without him is a very important advantage," he told Sky Sports.
"Sergio does not have a problem, but we thought 60 - 70 minutes and the way he plays always running it was we wanted, we wanted him to have more minutes but at this moment not 90 minutes."
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