That is the brutal verdict of Keane’s former Republic of Ireland team-mate Tony Cascarino.
It has emerged this week Ireland assistant manager Keane allegedly had a behind-the-scenes bust up with Arter back in May.
The former Manchester United captain is said to have called the 28-year-old a “p****” and a “c***” when he was receiving treatment for an injury.
Cascarino played alongside Keane on many occasions for his country during the 1990s and says Keane’s coaching style has always been a problem.
And he admits he is concerned for Ireland’s chances of qualifying for Euro 2020 because of it.
“Everyone keeps talking about Roy being this great professional, (that) he demands the highest standards,” ex-Chelsea and Aston Villa star Cascarino said on talkSPORT on Tuesday.
“Roy was never a great professional, I can promise you he was anything but. What he did and has done in the past as a coach is not professional.
“Having a go at players and being personnel, that’s the massive difference.
Roy Keane is alleged to have had a bust-up with Republic of Ireland midfielder Harry Arter (Image: GETTY)
Roy Keane has been torn apart by former Republic of Ireland star Tony Cascarino (Image: GETTY)
Roy was never a great professional, I can promise you he was anything but
“If your coach or No 2 says to you he’s trying to get better out of you and trying to improve you and has a go at you about making a mistake, every professional footballer would take it on the chin.
“But once it becomes personnel, and it has done on many, many occasions, and Roy has openly admitted that as well – he was asked to apologise to (Aiden) McGeady, (Jeff) Hendrick and (Daryl) Murphy back in 2016. So these things have been happening way too often.
“I don’t have any sympathy for Roy because I think a lot of times he has planned it to go for someone. He has a been in his bonnet about the way they act or what they’re doing.
“Roy gives you a look that you know he’s going to launch into someone and he did that to Mick McCarthy in 2002. It has been endless.
Tony Cascarino played alongside Roy Keane for the Republic of Ireland (Image: GETTY)
Harry Arter was allegedly having treatment when Republic of Ireland assistant Keane criticised him (Image: GETTY)
“It’s not good for Irish football and it’s totally not good for us I think leading up to the next Euros.”
A leaked WhatsApp audio of Republic of Ireland left-back Stephen Ward surfaced on Monday in which the Burnley and Ireland left-back talked about the clashes.
“Apparently he [Arter] was getting treatment in the treatment room and Roy walked in and was like, ‘When are you going to train you f**king p****?’” Ward said.
“Harry was like, ‘What?’, and he was like, ‘Any chance of you training?’.
Roy Keane has been defended by Republic of Ireland manager Martin O’Neill (Image: GETTY)
“He explained the situation again and Roy was going off going, ‘You’re a f**king p****, you’re a c***, you don’t even care, you don’t wanna train’.
“Harry was just going, ‘Roy, I’m not speaking to you like this. I’m not listening to you. You’re not the manager. You can’t say anything to me’.
“Apparently Roy was going mad getting worse and worse and Harry got up off the treatment bed and was walking back to his room.
“As he was walking back Roy was shouting down the corridor, ‘You’re a f***ing p****, you’re a c***, you have been all your life’ and that was really it lads.”
Roy Keane was coaching during Ireland’s draw with Poland (Image: GETTY)
Roy Keane has proved a divisive figure in Irish football (Image: GETTY)
However, Ward was not part of the squad back in May and manager Martin O’Neill says he has heard a different version of what exactly went on with Arter and also forward Jonathan Walters, another player Keane is alleged to have had an argument with.
“First of all, Stephen wasn’t there, he’s just picking up on things, something that we talked about at the beginning of the week,” O’Neill said.
“I think differences of what was said… a confrontation with Jon (Walters) and a confrontation with Harry. Jon is fine, absolutely fine. Harry perhaps not so fine.
“If you’re asking about Roy’s criticism of players, this is my responsibility. I will take full responsibility of anything that goes on.
Ireland drew 1-1 with Poland on Tuesday (Image: GETTY)
“These two confrontations took place months ago, they happen all the time, I will be astonished if there isn’t one between now and November.”
Ireland drew 1-1 with Poland on Tuesday night, with Aiden O’Brien putting O’Neill’s side in front on 53 minutes.
Poland bagged their equaliser with just three minutes remaining thanks to Mateusz Klich.
But O’Neill was happy with the performance as he now looks ahead to October’s Nations League games with Denmark and Wales.
“It was a brilliant effort by the players and we will step forward for the two games now next month,” said O’Neill.
“It was a great effort and it was just disappointing that we didn’t see it through.”