Audio has emerged of defender Stephen Ward apparently describing last May's incident.

Arter pulled out of Thursday's 4-1 Nations League defeat by Wales and Tuesday's friendly in Poland.

"Stephen wasn't there. He's just picking up on things," said O'Neill.

"[It is] something that we talked about at the beginning of the week - probably not anything more to really report."

O'Neill attributed the recording to Ward during Monday's news conference in Poland.

Keane's row with Arter was also reported to involve striker Jonathan Walters, who played against Wales before returning to his club Ipswich Town on Friday.

O'Neill said he accepted "full responsibility" for Keane's clash with Arter and Walters.

O'Neill defends 'brilliant' Keane

O'Neill denied suggestions that former Republic and Manchester United midfielder Keane has become a liability within the Republic management team.

He said: "In my time as a manager, I've chosen two brilliant, brilliant assistant managers, two characters, two world-class players: John Robertson and the young man himself, Roy Keane.

"They're different, but at the end of it all, none of them have ever let me down. John Robertson criticised players; Roy has a different way."

O'Neill also denied that Keane has a bad relationship with the players.

Stephen Ward will miss Tuesday's friendly because of injury after starting against Wales last Thursday

Injured Ward misses Poland trip

Burnley defender Ward played in the win over the Republic in Cardiff but has not made the trip to Wroclaw because of a foot injury.

O'Neill said of the recording: "Differences of what was said... a confrontation with Jon and a confrontation with Harry. Jon is fine, absolutely fine. Harry perhaps not so fine.

"But I said to you before, you'd have to ask if that is the complete reason why Harry is not participating in these games this time."

O'Neill said rows happen within the squad "all the time", adding: "I will be astonished if there isn't one between now and November."

'I had a row with Meyler on Friday'

Pointing to midfielder David Meyler sitting beside him at the news conference, O'Neill said they had a disagreement on Friday.

"I have got the utmost regard for him as a person," said O'Neill.

"As I said to him, I might have a difference of opinion about his ability, but that's not the point.

"For him to take the criticism I gave in front of the rest of the team was extremely strong. He's a strong person, a really strong person."

With Seamus Coleman ruled out of Tuesday's game by injury, Meyler is expected to come into the team as captain.