Turkey have two teenagers who together are worth more than most national teams. And Australia have to stop them on Sunday.

Kenan Yildiz and Arda Güler are both 21. They're valued at a combined $300 million — a conservative estimate, according to Transfermarkt, which ranks them as the two most expensive Turkish players of all time. Neither was born the last time Turkey played at a World Cup in 2002.

Yildiz wears the No.10 at Juventus, the iconic shirt once worn by Alessandro Del Piero and Roberto Baggio. Last season he scored 11 goals, set up nine others, and created 76 chances in Serie A — more than any player bar one. Juventus boss Luciano Spalletti called him "an alien. He's not a normal footballer."

He also nearly missed this match. Yildiz injured his calf at Juventus training, ruling him out of their final game. Darren Burgess, the former Socceroos fitness boss who now works at Juventus, helped manage the injury with Turkey's staff. After days of individual training, Yildiz has resumed sprints. But Turkey coach Vincenzo Montella hinted he might be used off the bench, saying he had "doubts" about some players.

If Yildiz is the rock star — this month he became the first man to appear on the cover of Vogue's Turkish edition — then Güler is the golden boy. He plays for Real Madrid, has nearly 18 million Instagram followers, and is Turkey's most recognisable athlete. His game is built on imagination and passing that others don't see.

Alessandro Circati, the Socceroos defender who faced Yildiz twice last season for Parma against Juventus, knows how dangerous he is. In their first meeting, Yildiz created two goals in a 2-0 win. Circati was helpless for the first — a cross that Jonathan David side-footed in from six yards — and was beaten again on a counter-attack.

"He's a great player. I just have to put it like that," Circati said. "His ability one-v-one, to get the ball, drive it ... I think he's Juventus' best player."

Circati hasn't faced Güler yet, but isn't fazed. "In every competition, bigger-name players don't always come out on top against better teams," he said.

Darren Burgess, who has worked at Liverpool and Arsenal, said he has never seen a player with Yildiz's ball control and dribbling up close. "He's the person that fans and players turn to, to produce something in tight games," Burgess said.

Turkey see themselves as "dark horses" of the tournament. And with two $300 million superstars leading the line, they have every reason to believe it.