The Daily Mail reports Diouf has been arrested on suspicion of violent disorder after a brawl at a Manchester nightclub left a man with serious injuries.
Anton Ferdinand was also interviewed by police under caution later on Sunday following the incident at the Circle Club. The 27-year-old QPR defender was not arrested.
Former Liverpool, Bolton and Blackburn forward Diouf, 31, was bailed until May 23. The Senegal forward now plays for Doncaster, who were relegated from the Championship on Saturday afternoon.