If there’s one person in football that you don’t want to get on the wrong side of it’s Roy Keane.

The former Manchester United captain may have retired 12 years ago but he still remains just as ferocious today.

Keane, who turned 47 last month, isn’t afraid to tell people exactly what he thinks, even if it upsets them - as we’ve seen on numerous occasions in his role as a TV pundit in recent years.

He seems permanently angry, for some bizarre reason, and always ready for an argument. It’s part of his make-up and one of the reasons, you suspect, why he was so successful as a footballer.

However, his fiery nature has led to Harry Arter pulling out of the Republic of Ireland national team’s most recent fixtures.

Arter, who is currently with Cardiff City on loan from Bournemouth, pulled out of the squad following a bust-up with the team’s assistant manager.

Martin O’Neill confirmed that Arter’s row with Keane may have been one of the reasons he had made himself unavailable for selection but little more was said about the matter.

Details emerge of what Keane said to Arter

However, Irish publication The Sunday World - per the Irish Independent - have now revealed some fascinating details about the ‘verbal assault’ from Keane that left Arter’s teammates ‘stunned’.

'A witness told the Sunday World how:

- After Arter and striker Jonathan Walters were told not to train by FAI medical staff due to injury concerns, Keane launched separate verbal tirades at both in the team hotel.

- Amid his meltdown, Keane called Arter "a w***ker and a p***k" and suggested he did not rate him as a player and would not pick him if he was Ireland manager.

- Arter didn't respond to Keane during the tirade, but Walters did snap back as the duo became embroiled in a heated exchange.

- Ireland manager O'Neill was not present to witness Keane's rants at either Arter or Walters.'

Witness: Keane went for it

It sounds like Keane absolutely lost the plot in that moment and flew off the handle, laying into Arter and overstepping the mark in the process.

"Keane went looking for the players and it’s clear that he was going to tell them what he thought of them," a witness told The Sunday World.

"If a player is told he should not train by doctors, he can't ignore that advice and possibly aggravate a problem. That's why everyone was confused about Keane's attitude.

"Keane went for it. He called Arter every name under the sun, but we should not be surprised by that and it is not the first time they have clashed in recent years.

"Arter didn't say much and just went back into his room and a few players went in with him, but no-one who witnessed that was surprised when he said he would not be coming back.

"Keane probably told O'Neill his version of events, but he must realise now that this was well over the top."

It’s hard to imagine Keane apologising for his actions but he might be under more pressure to do so after these details of the row went public.

Ireland were beaten 4-1 by Wales in their UEFA Nations League opener last Thursday.

The squad will take on Poland in a friendly on Tuesday night.