The former Liverpool and Blackburn man joined the Championship club on a non-contract basis and made his debut as a second-half substitute in Saturday's 4-0 pre-season win over Shrewsbury Town.
Warnock, who once infamously described Diouf as a "sewer rat" during his time in charge at QPR, has decided to bring in the Senegal man after holding positive talks with the African.
"I met him about six or seven weeks ago," explained Warnock.
"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.
"We're also short on the right-hand side. There's a not a lot of money without moving players out - there's a couple of Premiership lads I've looked at, but they're on a lot of money - so I thought we'd have a look."