The 31-year-old has joined Leeds on a non-contract basis, making his debut for the Whites in a 4-0 win over Shrewsbury Town on Saturday.
Warnock revealed that a conversation with Diouf provoked a change of heart that persuaded him to take a chance on the player.
He told Yorkshire Radio: "I met him about six or seven weeks ago. It wasn't a planned meeting, but we ended up having an hour-and-a-half chat and I told him what I disliked about him and he talked to me about the things that he's done in football.
"It opened my eyes in what I thought about him and nobody has said worse things about him than I have. It would have been easy for me not to bring him to the club but I've never been one to shirk a situation.
"A friend of mine, Micky Walker, who was at Doncaster Rovers, couldn't speak highly enough of him. He said he's good in the dressing room, he's excellent with the youngsters, and is a bit of a likeable rogue. And he told me his weaknesses."
Leeds begin their Championship campaign against Wolverhampton Wanderers on Saturday, August 18.