Melbourne Victory have revealed captain Carl Valeri will miss the rest of the 2015-16 A-League season as he recovers from an inflammatory condition affecting part of his brain.
Valeri, 31, has not played since the end of November after developing incoordination and balance problems.
The midfielder was later found to have a small part of his brain inflamed, with the cause of it still unknown.
However, the club confirmed on Thursday he would not take to the pitch again this season as he continues his recovery.
"Carl developed incoordination and balance problems eight weeks ago. Extensive tests and specialist neurological reviews have determined an isolated inflammatory process affecting a small part of the brain. The exact cause of this inflammation is unknown," said Victory club doctor Krishant Naidu.
"Carl's condition has continued to improve with treatment, but he has not recovered sufficiently to be able to return to football training.
"As such he will be unavailable for the remainder of the A-League season. The inflammation remains isolated and continues to decrease in size.
"We are optimistic that Carl will continue to make a full recovery. This is expected to take a few months. Carl will continue his rehabilitation under supervision and devote his energies to his recovery."
Valeri, who has made 52 appearances for Australia, said he is intent on returning to the field as soon as possible.
"It has been a frustrating time for me not being able to join my team-mates on the pitch for the last few months," the Victory skipper said.
"The doctors have been happy with the progress I've been making, but they believe it's the best thing for me to take the right amount of time to recover fully.
"I'm grateful to the club for taking the view that they have and I look forward to returning on a full-time basis and leading the team again.
"I also want to take this opportunity to thank everyone at Melbourne Victory and all the members and fans who have wished me well and respected my privacy during this time."
Victory have missed Valeri at times this season, but Kevin Muscat's men sit fourth in the A-League table.