The versatile Garcia, who played in two of Australia's matches at last year's World Cup finals, needs surgery on the recurring injury he sustained while playing for English club Hull City.
Teenager Oar, a lively left winger dubbed the "next Harry Kewell" who plays in Netherlands for Utrecht, was called up to replace him.
The Socceroos arrive in Dubai for a pre-tournament training camp on Monday and will play the United Arab Emirates in their final warm-up on Wednesday before leaving for Qatar on Thursday.
Australia, who reached the quarter-finals on their Asian Cup debut in 2007, play India in their first match of the tournament on January 10 and also face South Korea and Bahrain in Group C of the opening round.
Goalkeepers: Mark Schwarzer (Fulham), Brad Jones (Liverpool), Nathan Coe (Snderjysk Elitesport).
Defenders: David Carney (Blackpool), Lucas Neill (Galatasaray), Luke Wilkshire (Dynamo Moscow), Sasa Ognenovski (Seongnam Ilhwa), Jade North (Wellington Phoenix), Matthew Spiranovic (Urawa Reds) Jon McKain (Al Nassr).
Midfielders: Brett Emerton (Blackburn Rovers), Brett Holman (AZ Alkmaar), Carl Valeri (Sassuolo), Harry Kewell (Galatasaray), Jason Culina (Gold Coast United), Mile Jedinak (Genlerbirlii), Matt McKay (Brisbane Roar), Tommy Oar (Utrecht), Neil Kilkenny (Leeds United).
Forwards: Scott McDonald (Middlesbrough), Robbie Kruse (Melbourne Victory), Tim Cahill (Everton), Nathan Burns (AEK Athens).
