Melbourne Victory veteran Carl Valeri has been diagnosed with an inflammatory brain condition, the club announced on Tuesday.

Valeri, who has earned 52 Socceroos caps, has not played since November 28 due to illness, and tests have revealed the nature of the condition that is affecting his balance and co-ordination.

The 31-year-old Victory captain is responding well to initial treatments, club doctor Dr Krishand Naidu said via a statement, though the full results of extensive tests will not be known for another fortnight.

"Carl developed a medical condition two weeks ago that affects his balance and coordination. He had a viral upper respiratory tract infection in the week leading up to this," Dr Naidu said.

"Carl had a progressive loss of balance and coordination and became unable to train.

"He has had specialist reviews with an ear, nose and throat surgeon and a neurologist with extensive investigations.

"To date, these have revealed an inflammatory condition affecting part of his brain.

"These results will likely elucidate the exact nature of this illness.

"Carl will reintegrate into training in a graduated program as he continues to improve."

Muscat hopeful Valeri will play again this season

Valeri, 31, is in good spirits and has responded well to treatment of his inflammation, but has no idea when he will be able to play again.

And his condition leaves coach Kevin Muscat a man down, not knowing whether he can turn to an injury replacement player given the circumstances.

A day before Victory's mid-week match with Perth Glory, Muscat said he was focussed only on his skipper's health and recovery.

"He's in the best possible care and he'll have further tests," he said on Tuesday.

"We're very concerned but we're optimistic he'll be fine."

But Muscat could not guarantee Valeri would play again this season.

The championship-winning coach said he believed Valeri would "because I'm an optimist".

With three matches in eight days, Victory must push on without their skipper, beginning with the visit to nib Stadium on Wednesday.

Muscat revealed veteran striker Archie Thompson was close to making the trip, three months after suffering a medial ligament injury that has delayed his start to the campaign.

The A-League's all-time leading goal scorer will instead be left in Melbourne for a possible return in Saturday's derby.

"Archie wanted to play last week, that's how close he is," he said.

Muscat said no other players had put their hands up for a break before their duel with Melbourne City.

Muscat is in the unfamiliar position of needing to pick his squad up after consecutive losses but he refused to believe his squad was in a hole.

"The results haven't gone our way but we were good in Western Sydney," he said.

"On any other day that would have returned us three points.

"We didn't win so there's some areas to improve but the performance in general was very good."

ABC/AAP