Manchester City boss Pep Guardiola praised Red Star after their victory in Belgrade.
City won their final Champions League group 3-2 with a youthful line-up.
Guardiola said: "It was a hard-fought match, physically demanding with a lot of man-on-man contact.
"But I am happy with what we achieved and how the team performed. People sometimes write off these games as not essential for us, but it's the exact opposite. Every win counts.
"Today, with really young players, they played really good. And a demanding game because they played a lot of man-to-man, so aggressive, with so much speed up front. It was a proper football game with an exceptional crowd.
"Red Star are known for the pressure they project, both on the pitch and from the stands, and you can see that the people here love football."
