Diouf opened the scoring for the Lancashire club in the 17th minute but is understood to have spat at home supporters during his goal celebration. Crowd control stewards have supposedly taken down statements from a number of witnesses and reported the incident to referee Uriah Rennie.
The Senegal striker has just returned from a three match ban after a similar offence saw him guilty of spitting at the Portsmouth defender Arjan De Zeeuw in late November.
He has also been questioned by Teeside police officers after Bolton's game with Middlesbrough in the same month after a young Boro fan alleged that the African spat a sports drink at him after being substituted.
Ex-Lens man Diouf has been warned that he is on his last chance at Bolton, should these claims carry any foundation then the future will look even more bleak for the on loan Liverpool forward.