Roy Keane got into so many altercations with opponents during his professional career.

But it wasn't just opponents that Keane fell out with; he also had bust-ups with his own teammates.

It's very well known that Keane and Peter Schmeichel did not get on very well at all.

Keane also had a run-in with Gabriel Heinze during their time together at Manchester United.

The Argentine joined United in 2004. Shortly after his arrival, Heinze was confronted by Keane in the dressing room after a defeat.

Heinze dared to hit back and, according to the man himself, he was left unconscious.

Speaking to ESPN Argentina's 'Pura Quimica' in 2017, Heinze said: "We ended up losing 2-1. The team was disastrous. To be honest, I thought I had not played that badly.

"I'm the first one off the pitch when a game ends because I don't like to talk to anyone. I went straight to the changing room - I was the first in and Roy was next. I didn't speak much English then.

"I see that he [Keane] is staring at me and he says 'f--- off.' I knew that swear word because those are the first things you learn. He comes towards me and I tell him 'f--- off you,' and that is the last thing I remember. I didn't even have time to swing my arm..."

MANCHESTER -DECEMBER 19: Roy Keane of Manchester United shouting at his team mates during his return to action in the reserve match between Manchester United and Newcastle United held on December 19, 2002 at Old Trafford in Manchester, England. (Photo by Michael Steele/Getty Images)

Sir Alex Ferguson heard about the incident and spoke to Heinze about it.

"Ferguson called me up and told me that he knew what had happened," he added. "I asked him if I needed to apologise… I mean he was the biggest idol of Manchester United's history.

"He [Ferguson] said, 'no, Roy was like that.' But he told me not to worry because Roy had already forgotten about that episode."

Despite Ferguson's reassuring words, Heinze went into training 'very scared' about coming face-to-face with Keane again.

"We went to training and I was very scared," he continued. "I remember we both went for a ball and I was ready for anything but as the action happened Roy told me, 'beware -- what happens on the pitch stays on the pitch and what happens in the changing room ends there.'"

But despite the run-in, Heinze still has great respect for the Irishman.

"I've had an excellent relationship with him since that episode," he said. "He is an extraordinary man. He was one of the best captains the club ever had."