Onnuoha had joined the Black Cats on loan from Manchester City in the 2010/11 season, but did not get along with center back pair John Mensah.
In one game, the two had to fight forcing Steve Bruce to label them as "a bunch of p*ssies."
That season Sunderland finished a respectable 10th place.
"John Mensah and Nedum Onuoha were two assertive players in the locker room, not to mention aggressive," Mignolet told The Times.
"After one of them played a short return pass, the other decided to make amends and make him feel small at halftime. At least that was the intention.
“Our captain [Lee Cattermole] intervened and Bruce was called from another room where he was with his coaching staff.
"Bruce said, 'Let them fight properly. If they want to fight, let them fight. "There was nothing more than a little push and pull. Bruce said," See now. You are a bunch of p * ssies in the locker room and on the field. " Read Full Story