Everton ran out 3-0 winners in a dominant display as former Liverpool player Diouf was subject to a series of boos from the home crowd.
The winger was seemingly involved in a verbal altercation with a ball-boy during the first half of the game after the youngster appeared to throw an out-of-play ball towards him with particular venom.
The Senegalese international then directed words towards the individual bringing sarcastic cheers from the Everton faithful.
Diouf then suffered further abuse from home fans, and again when he went to take two corners in the area of the original incident.
After the match police interviewed Diouf at the stadium before the Blackburn team left the ground.
A spokesman for Merseyside Police said: "We are looking into an allegation that a 28-year-old man used racist language at the Everton match today."