Melbourne City have suffered a huge injury blow with Socceroos defender Ivan Franjic ruled out indefinitely.

Franjic has suffered a virus during pre-season, which has caused inflammation around his heart and he has been forced to cease all training.

The rare virus is expected to keep him sidelined for an extended period of time and City is unable toย name a return date.

โ€œIvan is currently under the care and assessment of a specialist cardiologist who has advised he will make a full recovery,โ€ the clubย said in a statement on Tuesday.

โ€œAt this stage the cardiologist and the club are unable to provide a time frame for Ivan's recovery.โ€

Franjic is into his second seasonย of a three-year deal with City.