Both Manchester City attacker Grealish and Arsenal midfielder Rice both were playing for Ireland's youth teams when O'Neill was in charge.
"Personally speaking, I couldn't care less," O'Neill expressed to 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 (Rice) 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."