The attacking midfielder has impressed in the English Championship with Portsmouth this season after winning the A-League Men's golden boot last year, but has yet to crack a full international debut with the Socceroos.
Segecic, 21, represented Australia at under-17, under-20 and under-23 levels, leaving Popovic to believe the emerging star was on the path for Socceroos selection after first being called into the national team camp at 21.
"I think we've done very well by the player and the player's decided to play for Croatia, and we wish them all the best," was Popovic's diplomatic line after naming a 26-man squad for upcoming friendlies against Cameroon and Curacao.
But, reading between the lines, Popovic made it clear he would never be held to ransom with his selections.
"If you're getting called up for Australia through the junior levels, then you get called up by the Socceroos, shouldn't that be enough (to show) that you're wanted?" Popovic said on Thursday.
"Should I promise a player at 20 or 21 that he has to play?
"We've got young players in this squad now who are promising that they're going to play and, if they don't, I have to fear that he will leave?
"It's probably better for Adrian that he's gone because I now haven't restricted him from going maybe to where he really wants to be."
Capped 58 times and regarded as one of Australia's greatest players, Popovic said there was no way he would have ever given up on wearing the Socceroos jumper so easily.
"Maybe times have changed and maybe I'm a bit behind times here," he said.
"But I know when I was 20 or 21, when I got called in the national team, if I didn't play, all I thought about was, 'OK, I love that environment, I want to play for Australia and I'll keep fighting and hope one day I get selected by the coach'.
"I wouldn't walk out and say, 'OK, I'll make a phone call and see who else wants me'.
Since taking the reins in 2024, Popovic is adamant he has never closed the door on young players' dreams of playing for the Socceroos.
"You can see by this squad, you can see by the last squads that we've selected - young players have a great opportunity with the Socceroos. That's clear," he said.
"But I don't know what else I'm supposed to do if any player that comes and says, 'If I don't play, I'm out'.
"Should I play that player, even though maybe at that moment, whether it's technically, tactically or a player's maybe ahead physically at that moment, so he shouldn't play because someone's told me he'll leave?"
