The Borussia Dortmund central defender has not featured for his country since 2013, when he expressed his frustration at their failure to qualify for the 2014 World Cup.
Subotic has since suffered a serious knee injury, but has nevertheless made 15 Bundesliga starts for Dortmund this season.
Discussions with Curcic – and Serbian Football Association vice-president Savo Milosevic – took place after Dortmund's 3-0 win over Schalke on Saturday, yet the 26-year-old will not feature in Serbia's squad to face Portugal in Euro 2016 qualifying later this month.
"After a sincere dialogue, it is clear that Subotic is not ready to return at the moment," said Curcic. "The talk with Subotic was just one of many with those who lead the many potential teams.
"The match against Portugal is almost upon us and to me it is important to know which players I have so I can prepare for the upcoming duel.
"Serbia has several options in all places and it is up to me to choose the best one for achieving our ambitions."
Subotic has left the door open to feature for his country again, but will first focus on overcoming any doubts about his troublesome knee.
"It is still important to work on a full recovery from the severe injuries that I had last season that saw me take a nine-month break from football," he said.
"It is true that I came back and am playing, but still I do daily exercises to strengthen the knee.
"Additional engagement around the national team at this point would not be the best option for my condition."
