"We have to win, even more so because the title is slipping further and further away, and we have to make sure we take fourth place," Aguero told British media.
"We want the title but we have to take into account that United are right behind us and it will be a tough game. We will have to play intensely."
The fixture may not be the kind of title-deciding clash enjoyed by both sets of fans in earlier seasons, but losing will still hurt.
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City can kill off United's chances of qualifying for the Champions League with a home win, while defeat will almost certainly end their faint hopes of winning the title.
"At one point United were huge," Aguero said. "City have invested a lot of money to bring in quality players, and that has levelled the playing field.
"I don't know what is happening at United, I focus on City and Sunday. We are thinking about winning and nothing else."
Captain Vincent Kompany will miss the game after suffering a repeat of a calf injury in Tuesday's Champions League draw with Dynamo Kiev that saw City progress to the quarter-finals of the competition for the first time.
(Reporting by Simon Jennings in Bengaluru; Editing by John O'Brien)
