Back in 2014, Roy Keane recalled an interesting story about Gabriel Heinze in his autobiography when they played together at Manchester United.
Heinze was signed by Sir Alex Ferguson for £6.9 million in 2004 and made an immediate impression with his aggression in training.
And according to Keane, while the Argentine was a "good guy", he also had a nasty streak, describing him as a "nasty f***er".
"He was a nasty fu**er - nasty in training," Keane wrote. "We were playing Spurs at home the next day, and we'd always have light training the day before a home game.
"But it got a bit nasty and it ended up with myself and Gabby (Heinze) having a few tackles on each other.
"He kneed me on the side of my leg and, being the hero that I am, I kept my mouth shut. I didn't want to go in for treatment, but I was in agony."
Keane has never been one to keep quiet, but knowing the sort of person Heinze was, he thought it best to not retaliate.
However, according to Heinze himself, there was one occasion where Keane couldn't help but lose his temper with him - big time.
In an interview on Argentine television, as relayed by Reddit user kiwwi191, the ex-defender made the sensational claim that Keane once knocked him out after a game United lost.
No, seriously. According to Heinze, he and Keane clashed in the dressing room and was floored after telling his captain: "F*** off, you". Here's what he said.
HEINZE: "We lost a game and I went in the dressing room first and Roy Keane was second. I liked to go first after the game; I didn't want to speak to anyone as we lost.
"I didn't understand English, just the bad words. I heard my name and "f*** off" by Roy Keane, the best player.
"I knew that was bad so I stood up to him, this idol of Manchester, this great guy who everyone loved, and replied: "F*** off, you". I don't remember what happened next."
INTERVIEWER: "Did he punch you? Knock you out?"
HEINZE: "Yes. Yes."
Wow. Never before has this story been told, but it's absolutely insane - and yet very believable. Remind us to never mess with Keane.
Do YOU want to write for GiveMeSport? Get started today by signing-up and submitting an article HERE: http://gms.to/writeforgms