United defender Rojo knows all about Aguero's prowess in front of goal as the duo are international team-mates with Argentina.
Aguero has scored nine times in nine Premier League outings this season for defending champions City and Rojo is well aware that stopping the 26-year-old from adding to that tally this weekend is a big ask.
"It's crucial to defend well against Sergio," Rojo told MUTV as he prepares for his first taste of a Manchester derby.
"Everyone knows he is a very fast player who can inflict damage.
"He's very good at getting into dangerous positions. You need to be very focused and concentrated on his movement and be very aware of where he is and where he might put himself.
"You need to do throughout the 90 minutes."
A victory at the Etihad Stadium on Sunday would hoist United one point behind City.
Rojo added: "Sunday's game is very important.
"City are a direct rival in the league.
"A win would be very important for confidence for the next few matches and would help us in a big way to carry on amassing points."
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