Sydney FC have been dealt a cruel blow to their title aspirations with striker Corey Gameiro suffering a suspected season-ending knee injury while on international duty.

The 21-year-old is undergoing scans to confirm the injury but the club was notified by the FFA medical staff that he almost certainly ruptured his anterior cruciate ligament .

It is understood Gameiro tore his ACL while playing for Australia against South Korea in an Under-23 match. Sydney FC coach Graham Arnold was devastated with the news that one of the clubs most promising players will likely require a full knee reconstruction.

"Bad news is Corey Gameiro looks like he's done his ACL with the Olyroos," Arnold said. "At this moment he's with the doctors getting a scan. Medical staff from the FFA rang me straight after the game and [they are] eighty per cent certain [it is a torn ACL]."

May be gone for season: Corey Gameiro suffered an injury to his ACL. Credit:Getty Images

Gameiro was in stellar form this season having scored 12 goals in preseason and two in the A-League.