MELBOURNE, AUSTRALIA - APRIL 13: Ivan Franjic of Melbourne City controls the ball during a Melbourne City A-League training session at City Football Academy on April 13, 2016 in Melbourne, Australia. (Photo by Robert Cianflone/Getty Images)

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 to name a return date.

“Ivan is currently under the care and assessment of a specialist cardiologist who has advised he will make a full recovery,” the club said in a statement on Tuesday.

“At this stage the cardiologist and the club are unable to provide a time frame for Ivan’s recovery.”

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