The one-cap Socceroo has joined Sydney FC on a loan move from Scottish Premier League side Motherwell FC, ahead of Australia's final friendlies next month.
Stamatelopoulos had struggled for game time at Motherwell, starting in just nine matches this season and left as an unused substitute in four of his last five.
The 26-year-old has never played under Popovic and earned his Socceroos debut in 2024 after his stunning campaign with the Newcastle Jets impressed then-national team boss Graham Arnold.
Scoring 17 goals in 25 games for the Jets during the 2023/24 season, Stamatelopoulos debuted on the international stage in Australia's 5-0 World Cup qualifier win over Palestine.
Stamatelopoulos, a former Western United and Adelaide United player, moved to Motherwell in July 2024, scoring 12 goals from 45 games.
But the Adelaide-born striker will have his work cut out for him ahead of the Socceroos' final World Cup warm-ups against Cameroon in Sydney and Curacao in Melbourne next month.
Mitch Duke is among those jostling for the No.9 role under Popovic and had also sealed a return to the A-League, moving to Macarthur FC.
"After my time overseas, this is a fantastic opportunity for me and one I'm ready to embrace," Stamatelopoulos said in a Sydney FC club statement.
Stamatelopoulos joins Ufuk Talay's Sky Blues as much-needed firepower, with an option to make the move permanent.
Sydney FC have slipped to third (25 points) after jostling with Auckland FC for the top spot.
Auckland are second (28) with a red-hot Jets outfit (30) leaping ahead to lead the league.
"Apostolos adds real quality and competition to our attacking group," Talay said.
"He's a strong centre-forward with an excellent work rate, intelligent movement in the box and a proven ability to score goals in the A-League and overseas.
"His experience will be very valuable for us as we continue pushing towards the business end of the season.
"Competition for places is critical in a successful squad, and his arrival lifts the level of our entire front line."
Slated to arrive in Sydney on Wednesday, Stamatelopoulos will join training on Friday ahead of the club's home match against Adelaide on Saturday.
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