It has been reported that Roy Keane launched a verbal attack on Harry Arter last June after the Cardiff City midfielder was advised by medical staff to sit out training.
News emerged recently that Arter has stepped away from international duty and a falling-out with assistant manager Keane given as the reason.
The Sunday World reported at the weekend that the bust-up happened in June after team medics told Arter to give training a miss due to injury.
"If a player is told he should not train by doctors, he can't ignore that advice and possibly aggravate a problem," according to a source quoted by the newspaper.
"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."
Ireland boss Martin O’Neill acknowledged Keane’s part in the midfielder’s absence from the current squad, but defended his number two.
Ireland were hammered 4-1 in Cardiff by Wales last week in their Nations League opener and they take on Poland in a friendly on Tuesday night.
It was reported that Keane also had words with striker Jonathan Walters for the same reason, sitting out training on medical advice, but Walters did report to Ireland camp last week.
