Karacic joins Melbourne City teenager Daniel Arzani as the bolters in the preliminary 32-man squad named on Monday that will be likely be trimmed to 26 names by mid May before the final 23 players will be selected by June 4.
"He is already the captain of his team, at 21-years-old".
Van Marwijk said he had quickly identified right back as a position where Australia had a lack of depth when he took over as coach earlier this year and had been alerted to Karacic's eligibility by assistant coach Ante Milicic.
And the Dutchman offered a strong hint Cahill could well be on the way to Russian Federation next month for a fourth consecutive World Cup, labelling the 38-year-old striker "a special case" after naming the country's all-time leading scorer in his extended 32-man squad.
His last club goal came for Melbourne City more than a year ago, though his brace against Syria in October saved Australia's World Cup hopes and booked the successful playoff berth against Honduras.
"Before March he didn't play every week", Van Marwijk said.
Australia will play two friendlies against Hungary and the Czech Republic next month before taking on France in the first game of the World Cup on June 16.
Long Island weather: Partly sunny, highs in mid-60s
There is a chance for a rain shower or two Thursday night into Friday morning as a cold front will slide through the state. There is a dense fog advisory for counties north and west of Harrisburg, stretching from Johnstown to Williamsport.
'He plays only right back and we don't have a lot of players in that position.it's a position we discuss a lot, ' van Marwijk said. "I had a good experience with the 26 players in the 10 days that I worked with them, so I had no reason not to nominate them again. He plays only right back", he said.
Zagreb-born Fran Karacic, who plays for Lokomotiva in the Croatian first division, has been named in the Socceroos squad on Monday.
Arzani and Karačić are two of six new faces in the squad, with Alex Gersbach, Apostolos Giannou, Mitchell Langerak, and Jamie Maclaren also included. "But we have since seen other players so there will be a few new names in the squad".
Australia have been drawn into World Cup group C alongside France, Peru and Denmark.
Midfielders - Josh Brillante (Sydney FC), Mile Jedinak (Aston Villa, England), Jackson Irvine (Hull City, England), Robbie Kruse (Bochum, Germany), Massimo Luongo (Queens Park Rangers, England), Mark Milligan (Al Ahli, Saudi Arabia), Aaron Mooy (Huddersfield Town, England), Tom Rogic (Celtic, Scotland), James Troisi (Melbourne Victory).
Forwards: Tim Cahill (Millwall/England), Tomi Juric (FC Luzern/Switzerland), Matthew Leckie (Hertha Berlin/Germany), Andrew Nabbout (Urawa Red Diamonds/Japan), Nikita Rukavytsya (Maccabi Haifa/Israel), Dimitri Petratos (Newcastle Jets), Jamie Maclaren (Hibernian/Scotland), Daniel Arzani (Melbourne City), Apostolos Giannou (AEK Larnaca/Cyprus).