Reuters reports that the home supporters made monkey chants at the Gunners’ black players several times.
According to the news agency, one of their photographer at pitch level, heard dozens of home supporters make monkey chants towards Iwobi and Welbeck, as they neared a section of the stands when the ball went out of play.
The Premier League side were two goals down in Russia, despite winning the first leg 4-1 at the Emirates. But Welbeck scored 15 minutes from time, while Aaron Ramsey equalized in stoppage time, to ensure they progressed into the final four.
Iwobi came on as a second half substitute when he replaced Alexander Lacazette in the 77th minute.
The chants were heard when Welbeck celebrated his goal that brought Arsenal back into the game from 2-0 down.
A third Arsenal player who did not come off the substitute’s bench was targeted with the same chants after the final whistle, as he jogged to warm down on the pitch at the CSKA Arena.
The player, who Reuters was unable to identify, was also black.