A Reuters photographer says he heard monkey chants from CSKA fans directed at Iwobi.
Iwobi was a second-half substitute in the second clash which ended 2-2.
According to a Reuters witness, the Nigeria international and his Arsenal teammate, Danny Welbeck were targets of monkey chants from CSKA Moscow.
Reuters report that one of their photographer at the ground heard monkey chants from the CSKA Moscow fans towards Iwobi and Welbeck.
With Arsenal 2-0 behind and in the danger of surrendering their 3-0 lead from the first half, it was Welbeck who scored to bring the Gunners back in the game.
According to the report, the monkey chants were heard during Arsenal’s celebration of Welbeck’s goal.
Ahead of the 2018 FIFA World Cup in the summer, Russia face increased scrutiny over fan behaviour as they have pledged to crack down on racism.
UEFA, however, told Reuters that they have not gotten any report of racism during the Europa League game on Thursday.
The European football body has only opened disciplinary proceedings against CSKA Moscow for infractions including throwing objects and setting off fireworks.
The Russian Football Union and Arsenal have declined to comment on the report.