Melbourne Victory captain Carl Valeri has been diagnosed with an inflammatory condition affecting part of his brain.
The midfield defender has responded well to initial treatment since leaving training earlier this month with balance issues.
"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," club doctor Dr Krishant Naidu said.
The full results of further tests are not expected for another fortnight.