"I felt there was a good chance I was going to be left out of the World Cup squad altogether," he told Soccernet.
"When you looked at the facts, I had been playing well for Newcastle all season and we got into the top four of the Premiership, but it didn't seem to count for too much.
"Mick had a great loyalty to certain players and in some ways it was a good thing. It built up a team spirit and meant the players were always going to stand behind him. However, when you are on the outside looking in, as I was to an extent, it can be very frustrating.
"I never got my foot in the door of Mick's team and nothing I did for Newcastle was going to change that. Still, it's all in the past now and as far as I'm concerned I have a lot of unfinished business with Ireland. I want to kick start my career under the new manager."
And on the subject of a possible foreign successor for McCarthy he said: "That would be a massive change for Ireland and I am not convinced it is the right way to go. England have gone that route with Sven Goran Eriksson and it has worked, so maybe we all have to accept that times have changed, but I don't know if it would be right for us.
"The last two men in the Ireland job have been very down to earth, working class guys. If someone comes in from a foreign country with some radical new ideas, it will take a long time to get what he wants. And we haven't got that time because we need to start winning again soon if we want to qualify for Euro 2004."