The Three Lions have often poached Ireland’s best talent at a young age, including Jack Grealish and Declan Rice.
Both could have turned out for Ireland, with Manchester City midfielder Grealish playing for Ireland's under-17, under-18 and under-21 teams.
Arsenal's Rice represented Ireland at various youth levels, while even playing three friendlies for the senior team.
"Personally speaking, I couldn't care less," O'Neill told Jim White and Simon Jordan on talkSPORT.
"Secondly, if I did care, then I would think to myself, that Rice has chosen to play for England, what a terrible decision that's been! He's been to a couple of Euro finals and the Republic of Ireland haven't won a game.
"In fairness to Jack, Jack's father is English. At least I picked Rice for three games, he played three international matches at senior level for us. He played very well in the games.
"I would have loved for him to have made that decision. But the decision was always going to be playing for England. Also with Jack Grealish, he played at underage level for Ireland, but if it came to it, the big decision, he was always going to pick England."